In the crazy world of the environmentalist, the following logic holds:
Oil companies are subject to a supertax on top of corporation tax.
Oil companies operating West of Shetland do not have to pay this supertax.
Therefore oil companies operating West of Shetland are subsidised.
Therefore we should apply the supertax to all oil companies.
One can apply this logic elsewhere:
Rich people pay income tax at 40%.
Poor people pay income tax at 25%.
Therefore poor people are subsidised.
Therefore we should tax poor people at 40%.
I'm not sure our environmentalist friends have thought this through.