On the motorway there’s signs for services (rest stops) with all the major brands logos on, and maybe one or two billboards every 30 / 40 miles outside of city centres, then more as you come into a city centre.
I’ve also recently noticed a massive vertical screen on the side of a building near a busy interchange in my city (Manchester).
Public transport is littered with small adverts - on underground’s / metros there’s a lot of posters on escalators and buses have a lot inside, plus usually a big banner on the side (or a full skin of the bus but they’re fairly rare at least in my city).
Political advertising is capped at £20 million per party, but our newspapers do most of the real political propaganda come election time in terms of what stories they cover / who they endorse in their editorials (or sometimes they allow a major candidate to write one). The BBC also lets all parties with some traction do a 5 minute party political broadcast.
When I’ve watched some live US TV channels I’ve been amazed by how many “Vote X for Y, paid for by Z PAC” adverts there are and am thankful UK parties can’t spend anywhere near the same amount.