Try this site:

apps.rhs.org.uk

Go to 'gardening' , then go to 'advice' and you will find a section on plants suitable for wet soil.

Hope this helps. RHS sites are full of good advice.

Where are you in the UK? Is that area always boggy and damp, or is it just a result of lots of rain (if you're up north or in Scotland - certainly not anywhere south of that, we've had barely any rain)