Housing obviously, not least give buy-to-let landlords a kick. Some of them achieve an annual return of 16 percent.
Rail: as mentioned in another thread, millions of commuters, packed into shoddy rolling stock, would consider re-nationalisation or, at least, taking back the rail companies piecemeal as contracts come up for renewal. Would anyone burst into tears if Richard Branson was sent packing?
Break up the too-big-to-fail banks. Bring back Captain Mainwaring!
Proportional representation. The current threat to the union from Scots nationalism is an effect of the first-past-the-post system. For years Scotland has voted anti-Tory (there are more giant pandas in Scotland than Tory MPs) yet keep being saddled with a Tory government in London. This assumes the Scots don’t leave in September.
Broadband. Where I live in London I get c. 125 megabits per second from a fibre-optic cable. A friend in a Devon village gets 1-3 megabits per second… on a good day. His data arrives via a copper wire installed in the 1960s. Outside the urban centres Britain has third world internet.
What else?