I believe that Thomas was based on a Southern Eailway E class tank -- that is what Hornby used as the basis for their Thomas.
I hope none of the kids are disappointed when they see Emily (is this the Hornby version that's coming?) as the model is made from a quite different engine from the TV series.
If you have the original Thomas books, the locos can vary quite a bit. Awdry had great difficulty with the artists that the publishers assigned him -- one even refused to go to the station to see what they looked like.
Interesting read: The Thomas the Tank Engine Man, a biography of Awdry. Probably 10 years old now.