Hi Guest,
I don't think it is disallowed to show a corded poodle but I don't think you will get very far.:(
I have just looked at the Kennel Club's breed standard for Standard Poodles which says:
"Coat
Very profuse and dense; of good harsh texture. All short hair close, thick and curly. It is strongly recommended that the traditional lion clip be adhered to."
By that I interpret it to preferring the lion clip, but other clips can be used, including the corded look. However, as the lion clip is strongly recommended, don't expect anything if you go that way. Personally, I think it is the dog that should be judged, and not the look/cut of the overcoat it is wearing ;) However, it would be great fun to enter an exemption show with a corded poodle, just to see the reaction!

:p
Jean