Make it easier to build purpose-built holiday homes in nice places.
Build hotels, and look into hotel facilities which encourage year-round tourism (spa stuff, for example) regardless of weather, to avoid dramatic ups and downs in tourist numbers
Build more housing for locals. If there is concern about "There's no space!" have discussions about denser housing, to avoid encroaching on green fields and forests.
Increase the supply of nice places by making more towns and cities nicer (greenifying, pedestrianization schemes etc.)
Make tourists pay tourist taxes - reasonably fat ones, too, not just a few quid.
Consider running tourist buses and restricting cars firmly in areas that get overrun with cars in the summer, like Skye.
Allow two-tier pricing if desired by locals (however, it would help if the UK had a proper ID card system)
In local areas, there need to be clear and tough discussions about tradeoffs. Fewer tourists mean less money. Replacing tourists with "incomers who are long-term residents" may just mean loads of elderly people moving into "quaint" areas, using up tons of expensive services and clogging up the GP. Refusing to allow any building will mean a local housing crisis. Building more housing for both locals and newcomers involves the tradeoff of "sprawl vs tall" - either you need to accept more building on new land (sometimes green sites), or you will need to accept some taller and denser housing. I saw someone pouting about "zip lines" earlier on and saying "Why can't people just enjoy the area as it is already?" - but a zip line facility is the perfect example of the sort of thing that will attract people at other times of the year; if all you've got is a beach or whatever, you will end up empty at non-summer times of year, meaning there is more pressure to allow unrestricted numbers during the UK's very brief summer. I'm sensitive to the difficulties currently faced by people in these areas, but I also think it's only fair to point out that locals in these areas can sometimes be their own worst enemies, and demand "Santa wishlists" rather than policies - wanting tourism money without tourists, wanting housing but getting angry when anything has to be built, refusing to allow the building of tall buildings but not wanting green fields touched either, trying to block the development of leisure facilities that might make an area popular year-round, and then getting upset that "this place empties out in the summer and is like a ghost town."