Just an update.
Cleaned the Needles (in the top bit with the spring)
Cleaned the Float Needles also (which i'd gotten confused with something else briefly).
Tbh there wasn't really any crud anywhere but i gave the think a liberal soak in carb cleaner etc.
Put it back together (getting good at that now)and now it leaks slightly less than before i.e. it's gone back to how it was at the beginning of the problem (rapid droplets of fuel).
Interestingly also it smelt strongly of raw (as a pose to deep fried or baked) petrol when it was running (this is a new thing).
Going to book it into the garage tomorrow, either i've missed something simple the 4-5 times i've taken the carbs off or...well...missed something simple

If it's not one thing it's another eh?
Ant