The Poetry Society

They run a yearly poetry competition of which the closing date is 31st october you have to ask them for an submission form so that you can send your poems and the first prize is £5000 which is the highest poetry prize in the UK
The guidelines (well a few of the ones I know at least) are:
40 lines max.
No limit on words
Poems can not have been entered anywhere else and can not be submitted anywhere else for a year if chosen as a winner.
There is an entry fee of £6 for the first poem and £3 for each poem after that unless you are a member of the poetry society in which case your second poem is free.

More info can be found on their website: www.poetrysociety.org.uk