We had Gilbert Giggles as the party entertainer and I cannot recommend him highly enough. He had all the kids (and the parents who stayed behind) in fits of laughter. His strapline is 'master of disaster and highly skilled delusionist' and I cannot think of a better way to describe him.
His website is www.gilbertgiggles.co.uk
He is based in South East London but does travel with request. A word of warning though, he gets booked up quite far in advance.....
Hope this is helpful for someone.