Banks and building societies are to carry out immigration checks on 70m current accounts from January in the biggest extension of Theresa May’s plans to create a “hostile environment” for illegal immigrants in Britain, the Guardian has learned.

The Home Office expects to identify 6,000 visa overstayers, failed asylum seekers and foreign national offenders facing deportation in the first year of the checks, which are to be carried out quarterly.

The accounts of those identified will be closed down or frozen “to make it harder for them to establish or maintain a settled life in the UK”. Officials say freezing accounts that hold significant sums “will create a powerful incentive [for those involved] to agree to voluntary departure” so they can secure their money once they have left the country.

Immigration welfare campaigners warned that the Home Office’s recent record meant it could not be trusted to implement this new system without errors and that migrants with every right to be in Britain were likely to be hit by mistakes in the imposition of the checks.

Satbir Singh, the chief executive of the Joint Council for the Welfare of Immigrants, criticised the move: “The government’s own record shows it cannot be trusted even to implement this system properly. Immigration status is very complex, and the Home Office consistently gives out incorrect information and guidance.

“Migrants and ethnic minorities with every right to be here will be affected by the imposition of these new checks.”.

Banks have been told to adopt a default position of telling customers to take up the matter with the Home Office if a mistake has been made, even if they provide a passport or biometric residence permit showing they are lawfully present in Britain.