More than 19,000 migrants from eastern Europe have come to Kent since eight new countries joined the European Union in 2004.

A report examining their impact reveals 19,530 registered for work across the county; but also estimated as many as 50 per cent have already left. Polish nationals account for the highest number.

The report also found that at 84 per cent, employment rates among migrants from the new EU countries were among the highest of all immigrant groups. Very few claim state benefits and on average work about 46 hours a week.

Across Kent, on average there are about nine migrants from countries like Poland, Estonia and Slovakia per 1,000 residents, far lower than many other parts of Britain.

The highest ratio was in Gravesham, which has 2,145 migrant worker registrations in three years, or 15 migrants per 1,000 residents.

Swale was next highest, with 14 migrant workers per 1,000, followed by Dartford, with 13. Swale saw the largest number of registrations, 2,700. Thanet has the lowest number of migrants from the new EU countries. Just 860 registered for work.

The report says that the number of people arriving is falling and the number leaving rising, as economies improve in the home countries. That could leave some UK businesses facing recruitment difficulties.

Dr Danny Sriskandarajah, one of the report’s authors, said: “Migration from the new EU countries has happened on a staggering scale but seems to have been largely positive for all concerned.

Kent MP and shadow immigration minister Damian Green said: “There are good and bad things about large-scale immigration. The reason there are some problems is that failing to control the numbers maximises the strains and stresses on local authorities who have to provide extra services.”