How long was the bike sitting?
If it were mine, this is what I would do:
1. Drain the float bowls into a clear container & check for water or contaminants - if any found, also drain the tank and refill with fresh gas
2. Check the hidden filter, remove it, & install an inline filter between the fuel valve & carbs
3. Confirm spark at each plug
4. If any question about spark plug condition, replace both.
FWIW, in the USA, at my local Lowes, a can of Seafoam is approx. $8.00 USD (5 quid?)...good stuff.
