The British and French Governments are funding the Global Calais Project which targets those staying in squalid makeshift camps near Calais.
The immigrants - many of whom have paid people smugglers to help them reach the UK - are told they will be put on a flight home and given help worth 2,000 euros if they agree to go voluntarily.
The UK taxpayer's contribution, likely to run to millions of pounds, is to help the migrants set up a small business once they return to their homeland.
It also emerged last night that the Government is reconsidering funding joint flights with the French to take failed migrants home.
Last year the French pulled out of a plan to introduce charter flights to repatriate illegal Afghan migrants, citing humanitarian reasons.
The Home Office already funds payments worth £4,000 for failed asylum seekers living in the UK who agree to go home. But inducements are now on offer to people who have not even reached the UK.
Officials insist that any cash payments made to the migrants come from the French Government. However, the UK pays millions every year to the International Organisation for Migration, which is running the scheme. Last year the Home Office gave it almost £20million.