Let's go to the seaside

So if you live in north-west London, say, and you're not from Britain, and you want to go to the beach. Here's some recommendations (I guess they'd also work if you flew into London and stayed in a hotel if you had a car):
In Kent: you’ve got Dover (which is a bit of a dump – there’s the white cliffs and the castle, but the town itself is quite shabby, and don’t go anywhere near the ‘White Cliffs Experience’ which is a tourist attraction where you don’t get to see either the cliffs or the castle, and is thus a bit pointless).
Just down the coast from Dover is Folkestone. This is also a dump. Avoid.
But next to Folkestone is Hythe and Sandgate – which are nice small seaside towns; there’s the Royal Military Canal in Hythe which is really nice to walk alongside (as historical trivia goes, it was built in the 1800s to prevent a French invasion – which is baffling, because you figure if the French could cross the Channel, it wouldn’t be hard to get across another 10 metres of water).
Hythe has very good fish restaurants, a good promenade, that kind of thing, although it’s not as grand as Brighton – no pier, for example.
However, to get to any of these you have to get the M20, which is all the way over the other side of London for you. There’s also Whitstable (which is north Kent, nearish to Canterbury – so a bit closer to London, but it’s on the M2, which is not always as good a road as the M20 – oh, and one other bother is that every so often the M20 gets shut (usually due to a strike at the docks in Calais or similar)
Might therefore be better to head towards Poole, which is near Southampton (so take the M3) or I guess there’s also the Isle of Wight – but that’s more somewhere to go for a weekend rather than just the day.
Further away, Devon / Dorset / Cornwall all have great beaches, but that’s a bit further to go. If you wanted to go further afield, Dumfries (south west Scotland) is worth a visit – really unspoilt countryside, but that’s about a 6 hour drive, and as it’s further north the weather may be less reliable)