Banks and building societies will be forced to carry out immigration checks on 70m current accounts from January, according to reports.
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 scheme.
The measures are part of Prime Minister Theresa May's plans to create a “hostile environment” for illegal immigrants in Britain, and the accounts of those identified will be closed down or frozen.
An impact assessment was undertaken back in 2015 by HM Treasury along with the Home Office, the Ministry of Justice and the Financial Conduct Authority to weigh the effects these measures might have.
It said denying illegal immigrants access to banking services “will make it harder for them to establish or maintain a settled life in the UK and should incentivise voluntary departure”.
The impact assessment acknowledged that some illegal migrants, instead of leaving, might remain and work illegally on the “black economy”. However it concluded this was not a “significant issue” as such people are already living and working illegally by being in the UK.
A reader alerted the Guardian to the new measures after her husband spotted changes in his Barclays' current account terms and conditions.
The August 2017 update to Barclays' terms and conditions read: “We are currently required to check your immigration status when we open a new current account for you. From January 2018, we will also have to conduct these checks on all of your existing current accounts with us.”
The update adds anyone who no longer has permission to remain in the UK could see their current accounts closed along with “all other accounts, services, mortgages or loans (including any jointly held accounts or accounts where you are a signatory or beneficiary)”.
The new checks will require banks to run the identity of every current account holder against a Home Office-supplied database created by anti-fraud organisation Cifas.
The banks will then have a duty to notify the Home Office in case of a match, after which either the Home Office will seek a court order to freeze the account in cases where it is "necessary to exert some leverage", or in routine cases the bank will have to prevent access to the account.