As is so often the answer on here Decathlon wetsuits are good for occassional use but they had very limited stock the other week as my wife needed a new one.
South coast you are probably looking at 17 degrees sea temp so a shorty will be fine for an hour or two (everyone is different but that does me especially if the sun is out) We are at the top of Scotland this week so it is 12 degrees for that I use a 4/3 full wetsuit, they are £60 in Decathlon.
Decathlon shorties are nice and tight so little water movement, many cheap ones let water flow in and out too much