Does your carb have two mixture screws? I'm showing the X2 with the Tanaka engine only has an idle screw and not mixture screws. The UK version may be different, so let me know.
OK, give me a bit to locate the UK manual.
Being it only runs on choke, that indicates a lean condition. A lean condition is caused by not enough fuel or too much air. For the fuel items, check that your fuel filter is good and the fuel tank is clean with fresh fuel and good oil. If you put on a new carb, you should be ok. Many of those used plastic carbs and they tended to warp when they got old. There was nothing to do with them but put on a new one.
Even a new carb will have to be adjusted. The US version cannot be adjusted and I don't have the UK manual. One the adjustable models there will be a low speed jet and a high speed jet. Start the motor and warm it up. Turn the low speed jet counter-clockwise until it idles smoothly. Raise the rear so the wheel can spin safely and rev it up. Adjust the high speed jet so you get the most speed, then turn it counter-clockwise 1/8 of a turn.
Does it run properly now?
If not, you could have an air leak. This would be at the carb manifold where it bolts to the engine. The manifold is a bakelite material that will warp when old, or the gasket can fail. The other problem would be if one of the crankshaft seals failed. If you see oil behind the clutch or if you remove the recoil and see oil behind the flywheel, that seal has failed and must be replaced.
A 2-stroke motor must be air-tight to work properly, so any air leak will cause a condition where it won't run or where it can cause an engine failure from a lean condition.
Check those items and let me know if you are able to locate the problem.
Not a problem. Not everyone can know everything. That's why I'm here. Just check the things I mentioned and see if you can find the problem.
The rubber and plastic parts are bad but I've had good luck with the motors. Your motor was used as a brushcutter motor for many years before they put it on a scooter, so it does have a long history of being used. If you can't find a scooter repair shop, a chainsaw/brushcutter mechanic would be able to work on it.