Matchless G9 in Movies
It could reach a top speed of 137 km/h / 85 mph
Engine
The engine was a Air cooled cooled Parallel twin cylinder. A 66 x 72.8 mm stroke result in a displacement of just 498 cc / 30.4 cub in.. The engine features a 7.7:1 compression ratio.
Chassis
It came with a 3.25 x 19 in. front tire and a 3.50 x 19 in. rear tire. Stopping was achieved via Drum in the front and a Drum in the rear. The front suspension was a Teledraulic while the rear was equiped with a Swingarm, twin shocks and coil springs, oil dampers The G9 is fitted with a 17 L / 4.5 US gal fuel tank. The bike weighs just 181 kg / 400 lbs. The wheelbase is 1403 mm / 55.25 in. long.

Ich, ein Groupie
British definetly - Matchless ? http://motorbike-search-engine.co.uk/classic_bikes/matchless_g9_1955.jpg
It appears to have the earlier style non-full width front brake hub so is probably 1952-3. I think 1952 was the first year for the jampot rear suspension units. My first bike was a 1952 AJS 350 single - a bike similar in many respects to this one.