something that we could preferably catch a train to?
You could go to Brighton, Hove or any beach along the south coast line - its very do-able from London via the train as its a popular commuter route.
Alternatively, and my favourite, is to go to the Witterings - I love West Wittering http://www.westwitteringbeach.co.uk/ Its a fantastic place to visit
Depending on how far you want to travel, you could go to places like:
Southend on Sea which is tacky at its best, but there is something that I love about it
Clacton - similar to Southend
Whitstable is lovely and very different
The Norfolk coast is probably a bit too far but it is well worth the visit if you get a chance. about 10 years ago
Bournemouth is probably the best "Beach" within easy striking distance of London on the Train. Brighton is a great place but the beach is not so good, shingle rather than sand. Most of the South Coast is shingle. Although you can find some pretty deserted sandy areas around Chichester, Ford & climping. Climping is a really beautiful area but only if you're after tranquil countryside and sand dunes rather than tourist ammenities. about 10 years ago