I'd totally agree with Les - forget England, and head North.

I now live on the south coast, and coastline is BORING. I grew up near Newcastle so I'm rather based, but the north east coastline is fantasic. I got some great shots when I was back at xmas, without really trying (and if you're in Newcastle you've got to do the bridges).

Start in Tynemouth (the Priory ruins overlooks the river mouth), and then just head North along the coast into Scotland - you can't really help tripping over a castle or two.