If you don't typically have a need for a wider lens, rather than buy a cheap one, borrow or rent a nice one. I don't know who does rentals in the UK, but in the US, you can rent a 15mm ltd for a week for about $30 (maybe 50 with shipping). If you're not accustomed to using a wide angle lens, I dunno if I'd go any wider than that for landscapes. Indoor shots are a bit more forgiving (less chance of 1/3 of the image being parking lot).
But any lens can do landscapes. Just depends where you're standing. (IIRC Adam said in a thread somewhere that his favorite landscape lens was an 85mm). A wide angle can "get it all in" but that often means "get it all in really small and far away looking which makes it rather uninteresting, and oh, you stood with one foot forward, so you're going to need to crop the tip of your toe out of the shot"
Definitely second a good tripod and a remote. Also make sure you have a polarizing filter, and ideally some Neutral Density filter options (either a set or a variable one like the one PF just reviewed on the homepage). The sun does sometimes come out in wales and you don't want to end up with washed out details.