Matt,
how did you book the holiday - over the phone, internet or T.A. ?
Is it a Package you've booked. This normally comprises at least two of the following
a) Flights
b) Accommodation
c) Car Hire or Tours
If you've bought a package you shouyld look at this link
http://www.opsi.gov.uk/si/si1992/Uksi_19923288_en_1.htm
as it lists the regulations covering Package Tours. I've read it and cannot see anything particular about transfers but Clause 4 insists that the descriptive matter relating to Packages must not in any way be misleading. An "All-Inclusive" is deemed to refer typically to the meal plan. But you could argue, especially as you may be booking your first such all-inclusive package (and hence not an expert) that you considered this to include all aspects of the holiday being
flight, transfer to hotel, accommodation, food, maybe drinks, transfer back to airport and glight home.
The 'expert' seller of a product/service is expected to make such inclusions clear at the time the contract is made rather than the amateur 'purchaser' being expected to 'ask' the right questions.
When you did book, were you clearly informed of the extra transfer cost? If so, how - during the 'phone conversation ? If so, you will have accepted the condition but if you feel they did not explain this, demand a copy of the transcript of the recorded tape - they usually have one.
If you were first told of the extra transfer cost in writing, when - how long after the original booking. Most importantly, when do you fly as a tour op. is not permitted to make significant changes to the contract within 30 days prior to flying and I understand, not after the final balance has been paid.
There's a lot here I know but this is a complex issue. My experience dealing with T.O.'s is to be forwarned and forearmed (and if all else fails ring Ros Fernihough on 01922 621114 - a crackin' solicitor).
Mike