Sorry Ben, only just found this! Hope you, your brother and William got home ok the other night
Ok the update for now...in need of changing the throttle and choke cables, so Dad undid them (carb end) and for some reason took out the bolt which you thread your throttle cable into...then lost it down the back of the engine

Went along to Austin Watts (previously Dorchester Mini Centre) and got another...Dad has fitted everything back together this afternoon, only to find that the engine now won't fire!
Any suggestions - greatly appreciated!