The original improve comedy show, inspiration for the American version of the same name.
Some people would say that the American version of this show was the better of the two. However, I personally find the original my favorite of the two. While they are basically the same show, I just found the variety of comedians to be better, and for the show to have an all around better quality for the most part.
My recommendation: Unfortunately I do not think the UK version is aired on American television anymore. If you like the American version then take a look at the DVD release of the UK one as well.