Hi Jenn,
Firstly, you might like to head over to
the UK Boards which is where most of the Brits hang out...and plenty of them have been to
Disneyland Paris!
My own thoughts on it are...
If you are in London, the train may not be cheaper than the plane, but it is certainly easier. It takes just over 3 hours from central London to the Park gates, but obviously you don't have to worry about traveling to the airport or checking in early (20 minutes for the train) so whilst the train is faster overall and easier.
There are two trains - one that takes you direct from London to the Park and Disney hotels (the budget ones hotels are the Sante Fe & the Cheyenne - if you have DisneyClub, you can get a discount - all hotels are in walking distance to both parks though) or you can get the train from London to Paris (that way you can see a bit of the city too) however, Paris, like most capitals, isn't particularly cheap either! There are regular trains that run from Paris to the park, this will take you about half an hour as the park is actually a fair way outside the city, but it's an easy trip.
As I say, head over to the UK Boards (you'll need to re-register your user name before you can post) and ask on the Trip Planning Board, and I'm sure you'll get lots more opinions and input there
Penny