Protesters at St Thomas' highlight plight of hospital workers arrested last month

16 people were arrested by the police and the UK Borders Agency on Thursday 6 January in connection with fraud and identity offences at Guy's and St Thomas' NHS Foundation Trust.

Three of the arrested workers – a cleaner, a porter and a catering assistant – pleaded guilty to obtaining a pecuniary advantage by deception and being in possession of false identity documents. They were each sentenced to eight months' imprisonment the day after the arrests were made.

The Cleaners Defence Committee, No One Is Illegal, Hands off my Workmate and Latin American Workers' Association staged a protest outside St Thomas' Hospital during Friday evening's rush hour.

The campaigners claim that as many as 72 ancillary workers at the two hospitals have 'disappeared' in the last month.

The demonstration included chants of "No borders! No nations! Stop deportations!"

"Guy's and St Thomas' NHS Foundation Trust approached Southwark Police and the UK Border Agency for their assistance after trust staff identified a number of potential illegal workers," said a hospital spokesman.

"We have worked closely with them in following these matters up.

"We were disappointed that this problem arose, as we pride ourselves on carrying out thorough immigration and employment checks on all our staff. The majority of those involved were employed through an agency.

"Clearly the trust has no alternative but to uphold the law in these cases."