I had a little chat with the well-known voice actor; Jason Marsden on Twitter, he's never been to an event in the UK before and said he would absolutely love to be a guest at a UK event! He's just waiting for an invite... He's most well known for 90's cartoons such as Max Goof (A Goofy Movie), Garrett (Extreme Ghostbusters), Kovu (The Lion King), he's been in Tarzan, Batman, G.I.Joe, and loads more!
Please also think about inviting Tara Strong who Jason Marsden has worked with quite a lot (in programs such as Extreme Ghostbusters, Fairly Odd Parents, etc), I don't think she's been to the UK before either and she too has done the voices of many beloved 90's cartoons that we all remember and love! (mostly Cartoon Network and Nickelodeon). For the past few years she's been doing My Little Pony which is very popular.