Figures have suggested that the £2m 'Only In London' tourism campaign, which was launched by mayor Boris Johnson in spring 2009, could have generated up to £100m worth of extra revenue for the capital's economy.

According to the latest statistics from the Mayor of London's office, the number of overseas residents visiting the city in the third quarter of 2009 increased by 11 per cent to more than 2.1 million, compared with the same period during the previous year.

The Only In London campaign, which was backed by the London Development Agency and led by Visit London, was rolled out throughout the UK, Europe and North America during the summer in order to promote the city "unique" attractions.

An additional £400,000 was invested by the four central London boroughs - Camden, City of London, Westminster and Kensington and Chelsea, which represent around half of the capital's tourism spend.

Johnson also agreed to contribute a further £400,000 in November 2009 to extend the campaign's run until the end of March 2010.

"Clearly our campaign is hitting the mark. Despite tough times at home and abroad visitors continue to vote with their dollars, euros and pounds, maintaining London's position as the world's number one tourist destination," said Johnson.

"London's resilience and ability to buck the trend is down to many things, but I am confident that it has much to do with its unique heritage, a dynamic culture and so much to see and do whether you are here for a day, a week or longer."

Visit London chief executive Sally Chatterjee added: "The Only in London campaign provided us with a strong platform to promote the unique aspects of London to visitors at home and abroad. The feedback from visitors has been incredibly positive and is reflected in the outstanding economic benefit delivered by the campaign."