Its a Hampton By Hilton Hotel franchised out to
http://www.atlashotels.co.uk/our-hotels who also have numerous Holiday Inn Express Franchises.
They use 0871 numbers extensively as the first point of contact for their Hotels. EG.Sales . Which is perfectly legal and above board.
They are only required to offer a 01/02/03 customer service number to call them on if the customer has a customer service query EG. Booking Change. Which should normally appear on the booking form.
Hilton offer a FREEphone Number for Customer Service 0800 833775 (Option 2)
On the Holiday Inn Express Main Site they do say
(To modify or cancel an existing reservation call : 020 33 499657 )