The Britannia made its first appearance in the 'Minitrix N Gauge 1970/71' catalogue produced by Thernglade - a company created in order to take over the British production of the N Gauge models acquired by the German Trix Company in 1969.  Britannia was one of 6 British outline models on offer, although in the catalogue, the picture shows an image of Trix's own OO version of the model.  Nevertheless, the model was produced and continued to be in production throughout the majority of the Hornby Minitrix Involvement with Trix from 1973 until 1987.

Britannia was an amazingly popular model throughout the Hornby Minitrix era. A real heavy duty British steam locomotive, in N gauge. It is sensibly geared, has 3 driven axles and has positive pickups on two of the main drive wheels. All 6 loco axles are connected to the left, negative rail. The tender provides 2 positive and two earth pickups. It runs nicely around tracks, copes with the tight 9" radius of Peco track and even the tighter 7.7" radius of the Minitrix track system. The fixed axles are mounted inside brass bushes and the chassis clearance and the play in the conrods allow the axles to move laterally when negotiating these tight bends. In spite of the tiny disc wheels at the front and the ugly light green paint, this model looks smart on a layout. Like all Minitrix locos, the motor is mounted in the loco itself. The 6 drive wheels are all powered, kept in sync with brass gears on each wheel and metal idler gears. The pressed steel connecting rods and round piston rods are linked with a metal splined crankpin, and a tiny pressed steel cross-head oscillates smoothly back and forth on steel guide rails. As supplied, the end of the crank pin hovers over the centre of the axle, but since it has a spline fitting, it is possible to move it round a notch, to provide a more realistic steam valve motion.

The early version of the model came in green livery - a few shades lighter than the correct Brunswick Green of later models.  Sometime after 1980, the model was completely revamped adopting the chassis, the higher gearing and the front bogies that were used on the Mallard and later the Gresley, Boadicea and Flying Scotman models.  Apart from the paler green livery, this early version is easily distinguished from the later version by its solid disc front bogies, its metal crank pin, and its lower gearing (the size of the gear attached to the drive wheels is noticeably smaller that the later models).  German Minitrix continued to market the early model in their green/yellow card covered boxes as number 51-2037-00, or simply as 12037.  The Minitrix Number was N203 for both the early and later version of the Britannia.