Uh ?
Two things -
1. BP is a corporation not a state enterprise.
2. Your argument is a bit like saying that the USA should be responsible for the Union Carbide disaster that killed 1000s of Indians in Bhopal, or is responsible for the 167 deaths in 1988 on the North Sea oil rig run by Occidental.
BP will be fined for sure and I hope the company pays its dues (if it ever can) but this is nothing to do with the UK government.
Good points - that Union Carbide disaster was down right criminal. If a government should ever have to pay for a company disaster, that would have been the one.