I'm looking to get a second-hand kayak, preferably under £250, which I can use for river kayaking and sea kayaking - is there a particular kind I should go for? I've done a bit of river and sea kayaking but am certainly no expert. Cheers!
There's still a covid tax on most used sports equipment so there's no saying how much a good used boat will cost, however the class you're probably looking for are called crossover kayaks. The best known in the UK are the Wavesport Ethos, Dagger Katana and Pyranha Fusion.
They're all around 3m long, and have both a hatch and a skeg. In the grand scheme of things there's not much to choose between them, they're not perfect for any specific task but good enough for most.
The hatch means you can take enough kit for an overnight trip, the length means you can travel moderate distances while still being short enough for good maneuverability. They're also wide enough to be stable for a relative beginner.