Serpentine Gallery Tours

AVOID!!! We arrived at the hotel to stay 1 night (Saturday). We had booked using Expedia (also to be avoided). Upon arriving at the hotel, we were told by the person at the reception that we had not paid enough to Expedia and that if we were to stay at the price (already paid), he would not be making money. He requested that if we paid an extra £20 in cash we could stay but this sounded very dodgy to us so we declined. He asked us to call Expedia to tell them that we had not paid enough!!!!! We felt bullied, perplexed and blackmailed. He refused to give us the room at the price we had paid Expedia. We left the hotel as we could not face staying in such place after this experience. Expedia is not helping us (still ongoing). Nothing like this has happened to us before and I have never heard of such an instance whereby a booking is made online, pre-paid and then, when turning up at the hotel, the customer is asked for an extra payment. A new low?