Hotels in the capital were the worst hit in the the UK by the volcanic ash cloud travel chaos, despite a hike in room rates.
According to research by PKF Hotel Consultancy Services, occupancy in London was down 7.6%, from 76.3% in April 2009 to 82.5% in April 2010.
The struggling hotel sector had seen gradual improvements in recent months, until the ash cloud meant people were unable to travel to the capital and were forced to cancel bookings.
Some people were stranded in London, but this was not enough to offset the larger groups, such as those on conferences, who had to cancel, said PKF.
While hotels were charging 7.9% higher room rates, the yield, which measures room occupancy against the average achieved room rate, fell by 0.3% to £93.20.
Robert Barnard, partner for Hotel Consultancy Services at PKF, said: "The ash cloud impact was both positive and negative for hoteliers. Overall, the effects have not been too dramatic with the capital suffering the most."
Outside London, hotels saw a rise in occupancy 1.7% (to 68.1%), but a fall in room rates of 3.6%.
Some cities showed clear signs of recovery from last year. Birmingham saw a rise in occupancy of 4%, and a 5.6% increase in room rates to an average £61.03.
Manchester also saw a rise in occupancy last month, compared to April 2010, of 2.3%, but the average room rate decreased by 0.7% to 74.39.