Hotels in Coventry, Nottingham and Bristol saw the biggest room rate rise at 13, 11 and 9 per cent respectively while Aberdeen, Edinburgh and London actually saw rates drop by 25, 2 and 1 per cent.
Despite the national increase, 32 of the 40 most popular UK destinations recorded an average rate of £100 or less a night in 2015 with the seaside town of Blackpool found to offer the lowest price for rooms - an average of £64 per room per night.
The Rugby World Cup and the growing number of inbound visitors to the UK were said to be behind the price rise.
Isabelle Pinson, VP marketing for EMEA of the Hotels.com brand, said: "Last year was a fantastic year for visitors to the UK thanks to its thriving culture and abundance of international sporting events. Although we have seen a slight increase in the average room rate, prices paid by consumers are still great value overall."
The HPI uses data drawn from bookings made on hotels listed on the Hotels.com websites.
Average Nightly Hotel Prices Paid in the Top 10 Most Popular Destinations in the UK in 2015