Here’s an opinion that’s actually unpopular rather than simply controversial: domestic flights in the UK other than to Northern Ireland (which isn’t on the same island so fair enough) should be forbidden on the grounds their contribution to climate change cannot be justified.
Instead we should renationalise the railways by letting the franchises expire without renewing them and expand their capacity as far as we can. Instead of pissing around with HS2 we fuck the NIMBYs over with an Act of Parliament which they can’t swat away or delay and extend it all the way up to Scotland.