Report counts 400,000 temporary migrants

About 90,000 of the arrivals, all of whom stay for between one month and a year, came to work or study. The remainder come for a family visit or extended holiday.

The large number of arrivals, which come on top of the latest annual figure of 215,000 longer-term migrants moving to London, will fuel debates about immigration and council funding.

Local authority leaders claim that because short-term migrants are not counted in population statistics used to allocate funds, they are being forced to provide free services for tens of thousands of people.

Today's report by the National Statistics Office - commissioned in an attempt to assess the validity of these concerns - gives only limited support to the argument.

It shows that across the country, just over one million short-term migrants arrived in Britain during the year ending halfway through 2005. Of these, 393,000 came to London. The average length of stay is just under three months, but because departing migrants are replaced by new ones there is a permanent "stock" of 81,000 temporary visitors in the capital at any one time.

Today's figures also reveal, however, that a substantial number of existing residents - for whom councils do receive funding - go abroad for short periods each year. In London, the number spending between one month and a year abroad, despite officially resident in the capital, was 742,000 during the year ending in mid-2005.

The figures for the permanent "stock" of departing short-term migrants show more people leaving for a temporary spell abroad than the number arriving, with London's total of 114,000 significantly higher than the 81,000 incomers. The Home Office said the statistics show "more people are going out each year than coming in".

Colin Barrow, deputy leader of Westminster council, insisted that the concerns of authorities remained valid.

He also warned that the large number of illegal immigrants in the capital were not included in today's figures.