It's not where the money ends up, it's the justification for the tax being levied. The principal tax on petrol/DERV fuel is "road fuel duty", which is nominally intended to support the road transport infrastructure. The fact that the amounts collected far exceed the amounts spent is a separate issue.

>>Pretty well all taxes vanish into the same governmental pot, so there is no justification for some of us paying less per litre than others>> is a non-sequitur.