@rjberry: Thanks for that code! Think I'm going with ala.co.uk now!
I agree, pay extra £20 and get the better cover for peace of mind.
@davyk31: You have a very valid point about not keeping the car in 2-3 years.
I just spoke to an ala.co.uk representative online and all is clear now with this GAP business. RTI GAP pays the insurance difference to the amount on the invoice and Vehicle replacement GAP pays the insurance difference to the amount of getting a like for like new car.
I still have a few days before I collect my car so I'm going to think hard about which GAP type to get.