In the south of England, the main three centres are
- Vobster Quay in Summerset: lots of attractions to play on and a tunnel to swim though (at an angle, so a good buoyancy test). Max depth circa 35m. Vis is good in the winter, less so in the summer when the schools are busy. Has a burger van for sustenance. Well stocked shop with plenty of tech kit.
- Stoney Cove in Leicestershire: has a 35m pit with the "Hydrobox" and some other things to see. Most of the attractions (Stanegarth tug, bus, cars, other boats) are at 18m. Yellow "Nemo" submarine at 6m. It's a good place to practice navigation as the bottom's quite featureless. Some life including little crayfish. Nice restaurant / cafe which does not allow soggy divers to use. Hatch for cups of tea and bacon sarnies. Large well-stocked shop.
- NDAC -- National Diving and Activity Centre in Chepstow. This has a deep pit of about 75metres, but most of the "attractions" (planes, buses, helicopters tanks, containers, etc.) are above 28 metres with many around 12 metres. Of the three, NDAC's visibility is the best. Nice 'wet' restaurant to warm up in. Lots of other attractions; zip-wire, giant swing, offroad Segways. Used by a lot of more serious divers in the winter - my personal favourite.
There's a bunch of shallower lakes/quarries in the south-east, all max 10 metres and generally poor visibility and very cold in winter.
- Wraysbury next to Heathrow. Silty, very popular with schools in the summer, vis can be awful. Food's OK. Cheap £10. Good for navigation practice due to the vis. Don't arrive much before 0900 or you'll be sent away!
- Buckland Lake near Rochester. Chalk pit with some attractions - bus, plane, etc. Has a tunnel which novices should avoid. Drinks/food available. Cheap.
- Holborough Lake near Maidstone. Chalk pit with some attractions. Platforms are good for practice. Entry pretty easy. Gate opens at 0900. Generally has a queue.
When not in the winter practice period, sea diving is far more interesting than quarries & lakes. For novices, look at:
- Swanage Pier - the place where many people learned to dive. 6ish metres and easy access under the pier. Lots of boats go from there to the many local wrecks and drift dives. Highly recommended. Valentine Tanks is a nice 12ish metre dive on two WW2 tanks. The house wreck is the Kyarra; big with lots of life.
- Portland / Weymouth - Portland Harbour has lots of wrecks to explore in less than 20 metres of water and is good when it's too rough to go to sea. Lots of other wrecks available outside to suit all skill levels. Can also dive off of Chesil Beach if you want some exercise walking up the shingle with your kit on.
- Plymouth - some fantastic diving there. Lots of wrecks to explore for all skill levels which includes the Scylla (deliberately sunk for divers to play on), James Egan Lane, and many great drift dives. There's loads of boats and dive shops there who would buddy you up. One of the UK's premier dive locations.
- Brighton / Eastbourne - lots of boats going out from there exploring the hundreds of wrecks off the Sussex coast, again all levels available. Issue with that end is the chalky bottom can mess up the vis. So worth going out further. Eastbourne's local wreck is the Alaunia.
A little further afield, but some of the greatest experience you'll ever have underwater:
- diving with seals in the Farne Islands north of Newcastle. This is shallow diving at its best with granite rocks, kelp, and playing with those cute and playful seals. One for your diving bucket list.
- There's also lots of fantastic diving around the west coast of Scotland; around the Isle of Mull for example on the wreck of the Rondo at 60 degrees with the bow at the bottom in 50 metres and the rudder at 5 metres - a wreck for everyone to enjoy.
- And of course there's Scapa flow where much of the German fleet was skuttled
The sea on the south coast gets up to about 18C in the summer (July though October), and down to 7C in the winter. Visibility can be difficult in spring ("the May rot") and also after storms. The northern temperatures get up to about 12C, so drysuits are pretty much the tool for the job.
If you like wrecks, UK diving really is some of the best diving there is.