We had a similar problem for our cruise last September. We were flying to London (to meet my parents who were flying in from the US) and then having a driver take us to Dover. Our BMI flight from Teeside to London only allowed 44 pounds. We paid a surcharge that I believe was the same cost as the tickets (around 50 GBP) It seemed like a lot but we paid it and this year took the train to London for our cruise out of Dover!
Cheers, Pam