I don't think that the UK producing excess oil was a significant factor in keeping the oil price down; peak production was in 1985, when prices were falling due

I don't think that the UK producing excess oil was a significant factor in keeping the oil price down; peak production was in 1985, when prices were falling due to excess production (and large falls in demand) but Russia was a far bigger producer. The money was not invested it is true, but not producing it at that point (given the large investments) would probably not have been optimal either.