up to 40 percent probably originating from Russia, which implies misreporting by financial institutions, sophisticated tax avoidance, and the UK's "safe-haven" reputation. Hotels and restaurants The Blue Book 2013 reports that this industry added gross value of £36.6 billion to the UK economy in 2011. InterContinental Hotels Group (IHG), headquartered in Denham, Buckinghamshire, is currently the world's largest hotelier, owning and operating hotel brands such as InterContinental, Holiday Inn and Crowne Plaza. The international arm of Hilton Hotels, the world's fifth largest hotelier, used to be owned by Ladbrokes Plc, and was headquartered in Watford, Hertfordshire from 1987 to 2005. It was sold to Hilton Hotels Group of the US in December 2005. Informal A study in 2014 found that sex work and associated services added over £5 billion to the economy each year. Public administration and defence The Blue Book 2013 reports that this sector added gross value of £70.4 billion to the UK economy in 2011. Real estate and renting activities Notable real estate companies in the United Kingdom include British Land, Land Securities, and The Peel Group. The UK property market boomed for the seven years up to 2008, and in some areas property trebled in value over that period. The increase in property prices had a number of causes: low interest rates, credit growth, economic growth, rapid growth in buy-to-let property investment, foreign property investment in London and planning restrictions on the supply of new housing. In England and Wales between 1997 and 2016, average house prices increased by 259%, while earnings increased by 68%. An average home cost 3.6 times annual earnings in 1997 compared to 7.6 in 2016. Rent has nearly doubled as a share of GDP since 1985, and is now larger than the manufacturing sector. In 2014, rent and imputed rent – an estimate of how much home-owners would pay if they rented their home – accounted for 12.3% of GDP. Tourism With over 40 million visits in 2019, inbound tourism contributed £28.5 billion to the British economy, although just over half of that money was spent in London, which was the third most visited city in the world (21.7 million), behind second-placed Bangkok and first-placed Hong Kong. The UK's 10 most significant inbound tourism markets in 2019: Effects of the COVID-19 pandemic The travel restrictions and lockdowns necessitated by the pandemic negatively affected the entire hospitality/tourism section in 2020 with a