Really just a Mascot 1600 with the centre height raised from 8.5 to 10.5 inches (215 mm to 270 mm), the Mastiff 1400 was fitted with a headstock spindle increased in size and with a bore able to pass a 3.5-inch (90 mm) rather than a 3-inch (76 mm) bar. The hardened  nose of the spindle was also upgraded from an 8-in D.1 to an 11-in D.1 Camlock and, sensibly, the speeds were all reduced by between 10 and 12.5% to take account of the larger diameters and heavier workpieces the lathe was capable of handling.
At 13.5 inches (343 mm) wide the induction-hardened and ground-finish bed was identical to that used on the Mascot (as were all other mechanical parts, save for those already mentioned), and of the usual Colchester V-and-flat type, with separate pairs of ways for the carriage and tailstock. It was available in five lengths that gave 40, 60, 80, 100 and, at 10  inches more the longest Mascot, 110 inches (1000 mm, 1500 mm, 2000 mm, 2500 mm and 3000 mm) between centres. All the beds could be had either with or without a detachable gap piece that, if fitted, allowed material up to 32-inches (815 mm) in diameter and 8 inches (203 mm) thick to be swung on the (optional-extra) 20-inch and 27-inch (433 mm or 685 mm) diameter faceplates - the larger of the two being for use on gap-bed lathes only.
Because it sat on a flat section of the bed instead of a continuation of the V ways, the headstock was provided with a mechanism that allowed it to be adjusted laterally -  though before altering the factory setting the owner was strongly cautioned to consult the (very comprehensive) owner's manual.
Designed in conjunction with the British Machine Tool Industry Research Association the headstock spindle could pass a 3-inch diameter bar and had a hardened 11-in D1 Camlock nose; all the gears in the headstock (and not just those responsible for the main drive as on less heavily stressed Colchester models) were hardened and ground finished on Reishauer machines. 16 speeds were available, from 18 to 1400 rpm and, because of the high top speed and the capacity of the lathe, the makers warned against other than the use of the dynamically balanced, ductile-iron chucks with hardened scrolls that had been specially commissioned from Burnerd; if you want to mount a new chuck on your Mascot 1600 it would be unwise to fit anything other than one recommended by a reputable Western manufacturer.  You are welcome to email for advice as to what might be most suitable, 
Concentrically mounted paddle levers on the front face of the headstock selected the spindle speeds and worked through an ingenious and compact mechanism, with (for a machine tool) an almost foolproof system of colour coding to indicate the settings. All versions were fitted with a 12.5 hp (9.3kw) motor mounted inside the headstock-end plinth on an adjustable plate that drove up to the headstock through 4 V belts into a shaft on which were mounted two easily-adjusted, oil-immersed, forward and reversing clutches. On the same shaft, at the opposite end to the input pulley, was a Matrix multi-disc brake; it could be adjusted so that, in production work, the spindle could be brought to a very rapid stop or, for ordinary use, set so that the braking effect was less pronounced and the workpiece was able to be "inched" round by gentle use of the control levers. Once the spindle speeds had been selected and the motor switched on by the headstock-mounted push-button starter the spindle control was by two levers: one pivoted from the right-hand apron wall and the other up against the inner face of the headstock; both worked through a 'third shaft'  (parallel and below the feed shaft and leadscrew) that was connected by links to a cross shaft that passed through the bed just in front of the headstock. The apron lever gave a stop, forward and reverse action the other just a reverse and stop; in conjunction with the headstock-mounted clutches, the brake and electrical switches this easily-operated and safe system allowed the operator to control the spindle from either the vicinity of the toolpost or the headstock - and all whilst the motor was left running so that the minimum of time was wasted waiting for speed to build up (it allowed an unladen 12-inch diameter 3-jaw chuck to be accelerated from rest to 1195 rpm in 6 to 7 seconds and braked to a halt in approximately the same time). The lathe was also fitted with a headstock-mounted emergency stop button that operated through the obligatory "no-volt" release (to prevent the motor restarting after a power cut), and a motor-run warning light to alert the hard-of-hearing, or those working in a noisy environment, that things were "active" and the controls should not to be casually played with..
The lubrication arrangements for the headstock reflected the hard work the lathe expected to perform and consisted of an impellor-type pump (driven from an extension to the main-motor spindle) that was mounted on a oil tank fitted inside the headstock-end plinth. From the tank the oil was lifted to a "distributor block" fastened beneath  headstock the headstock's top cover and from there by pipes to the required locations. A flow-indicator sight-glass was fitted to the front face of the headstock to allow the operator to check that the lubricant was flowing correctly.
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Totally enclosed, the dual Metric/English screwcutting gearbox was lubricated by an oil bath and fitted with hardened and ground gears running on ball-race supported shafts. Three conventional levers, and a 6-position joystick that moved into radial slots around a circle, swapped the ratios. The box was able to generate a wide range of pitches without dismounting or changing any of the changewheels; the range of threads comprised: 40 Metric from 0.4 mm to 14.0 mm; 18 Module from 0.3 to 3.5m; 38 English from 2 to 72 t.p.i. and 27 Diametral from 8 to 60 D.P.  The range of sliding feeds varied from 0.002" to 0.032" (0.06 mm to 1.0 mm) and surfacing feeds at half those rates (and thus) from 0.001" to 0.016" (0.03 mm  to 0.5 mm) - all per revolution of the spindle.
Doubled walled, the apron had all its shafts supported on ball bearing at each end and the gears hardened and ground; the base was closed off to form an oil bath to splash lubricate the internals and, at the top of the front face, just to the right of cross-feed screw, was a rod that needed pushing in to operate a plunger pump to feed the same lubricant to the bed, cross-slide ways and cross-feed nut.
Selected by a push/pull button, the power feeds were positively engaged by a lever that allowed the feed to be stopped instantly, regardless of how deep and heavy the cut. A second push/pull button provided a means of reversing either feed - with a knurled-edge dial, on the apron's right-hand face, to allow the operator to adjust the trip force that disengaged the feed as it was moving to either left or right. This arrangement providing a handy means of obtaining maximum accuracy when turning up to a shoulder length. A thread-dial indicator was fitted as standard.
The carriage traverse handwheel could be pulled out to disengage it when power feeds were being used - a feature that was included from the very first models.
Machined all over, the compound slide rest was fitted with taper gib strips that allowed a very precise fit to be obtained - and gave far superior support in comparison with the cheaper "loose-strip" type. The 11-inch travel cross slide was especially wide and fitted with a cross-feed screw that could be adjusted to reduce backlash; although the slide was devoid of T slots and tapped holes - and so appeared, at a glance, to be incapable of mounting any accessories - the edges of the slide were machines to accept slide-on T-slotted and plain blocks that could hold a variety of items including hydraulic profiling units, and parting-off and other special tools.
With 9-inches of  travel, the set-over tailstock's hardened and honed No. 5 Morse taper barrel wasengraved with metric and inch graduations and carried a useful zeroing micrometer dial on the feed handwheel.
Constructed around two heavy cast-iron plinths, the stand had a deep slide-out chip tray between them. Surprisingly, it offered no storage at all, in either plinths or centre section, even though this would not have been difficult to engineer - and would have made life both easier and more productive for the operator.
All but the most perverse would have been happy with the combination of feed and leadscrew combinations offered by the maker, for the lathe was available with an English-pitch leadscrew with feed screw micrometer dial graduations in inches or millimetres, or with a Metric leadscrew
Standard equipment was fairly sparse (no 3-jaw was supplied) and consisted of a centre adapter to sleeve down the spindle nose, two No. 5 Morse centres, a simple slotted toolblock to accept one turning tool, driving plate, thread-dial indicator, spanners, oil can, an accuracy and inspection and a very useful combined instruction and parts book that showed the whole machine as a set of exploded component diagrams.
Accessories included both a dynamically balanced "Super-precision" ductile-iron 12.5-inch (315 mm) 3-jaw chuck with a hardened and ground scroll and a 16-inch (405 mm) ductile-iron heavy-duty 4-jaw chuck both specially made by the Burnerd company. A chuck guard, a telescopic taper turning attachment, a 20-inch (430 mm) faceplate for use on straight-bed lathes and a 27-inch (686 mm) faceplate for gap-bed models, a zeroing  micrometer dial on the carriage handwheel; a single-type bed stop, a 5-position indexing bed stop and a micrometer bed stops; a fixed steady with a capacity of 9 inches and a choice of plain or roller-bearing fingers; a 3-inch capacity travelling steady with a choice of plain or roller-bearing fingers; 4-way automatic ratchet-indexing and Dickson-type quick-set toolposts; dual metric and inch micrometer dials, a "longitudinal-travel" dial indicator, an Ainjest quick-threader attachment, T-slotted and plain blocks to locate over the cross slide and mount standard or quick-set rear toolholders, a high-precision, heavy-duty rotating centre, a low-volt light unit and a full-length splash back.
The 40-inch between-centres Mastiff 1400 was 98 inches (2520 mm) long and weighed 5110 lbs (2320 kg)
the 60-inch between-centres  lathe was 118 (3030 mm) inches long and weighed 5440 lbs (2470 kg)
the 80-inch between-centres lathe was 138 inches (3535 mm) long and weighed 5770 lbs (2620 kg)
the 100-inch between-centres version was 158 inches (4045 mm) long and weighed 6350 lbs (2880 kg)
the 120-inch between-centres version was 178 inches (4045 mm) long and weighed 7160 lbs (3250 kg)
All were the same width - approximately 42 inches (1070 mm) from front to back.
Details of the Mastiff 1400 replacement, the Mastiff VS1800 can be seen here.

Three conventional levers - clamped to each of the three shafts at the top of the inner plate - together with a 6-position joystick that moved into radial slots around a circle, swapped the screwcutting gearbox ratios.

Double leadscrew clasp nuts in V-way housings.

The apron was doubled walled, with its shafts supported on ball bearing at each end and the gears all hardened and ground; the base was closed off to form an oil bath to splash lubricate the internals and at the top of the front face, just to the right of cross-feed screw, was a rod that pushed in to operate a plunger pump to feed the same lubricant to the bed, cross-slide ways and cross-feed nut.
The power feeds were selected by a push/pull button and positively engaged by a lever that allowed the feed to be stopped instantly regardless of how deep and heavy the cut was. A second push/pull button provided a means of reversing the feeds.