Thank you all again for the advice. So I got stuck in and SUCCESS!! I now have a leak free fuel supply, thanks to the advice on here. This is what I did:
Replaced the jubilee clips with petrol pipe clips (Halfords 12-14mm) and, confirm, the fuel pipes are already nice and tight on all the spigots before using the clips.
Replaced the fibre washers on the fuel pipes banjo to float chamber and float chamber to jet block connections.
Checked and re-tightened the jet block.
Used Permatex Form A Gasket Cement on the threads for the reducers to the tank and the fuel taps to the reducers, as these won’t be coming off again any time soon. Word of warning - this is properly sticky stuff, use gloves when you’re applying it as it’s a bugger to get off skin.
Used PTFE tape on the fuel line to tap connections, as they will need to come off more regularly to take the tank off for service access, plus the taps and the connections are all new.