Naturalisation programmes have been carried out by a number of European countries. Since 1981 there have been more than 20 "regularisations" in France, Belgium, Greece, Italy, Luxembourg, Portugal and Spain. The largest and most recent was Spain's in 2005, which regularised 700,000.

The Home Office estimates there are around 500,000 "illegal immigrants", a combination of visa overstayers and refused asylum seekers, and admits it does not have the resources to deport them (current deportations run at 25,000 a year).

Strangers into Citizens has been highlighting the plight of what it calls the "shadow people", who are condemned - often for years - to a limbo of fear and furtiveness. Most long-term overstayers work and pay taxes, using false IDs. Refused asylum seekers - many of whom are unwilling or unable to return - often face destitution because they are unable to work. A number of the stories have been collected on www.strangersintocitizens.org.uk.

The campaign is holding a National Day of Action and Celebration on 7 May, following a Mass at Westminster Cathedral celebrated by Cardinal Cormac Murphy-O'Connor and London's other Catholic bishops. Among the speakers at a rally in Trafalgar Square will be Baroness Shirley Williams, Jack Dromey, deputy general-secretary of the TGWU, and the Anglican Bishop of Southwark, Tom Butler.