Europe dictates a minimum tax level for energy products; states can tax as high as they like.

Not sure if there is an equivalent on alcohol and tobacco, but I suspect not.

On the environmental issue, it's worth remembering that recreational marine use accounts for just 0.05% of the UK's total diesel consumption (if I remember rightly). So even forcing half of the country's boaters off the water would have a miniscule impact on the UK's climate change targets.