Porters, cleaners and caterers employed by outsourcing giant ISS are due to take four days of industrial action from 29 November across four sites at Croydon and South London & Maudsley NHS trusts - Croydon University Hospital, Maudsley Hospital, Lewisham Hospital's Ladywell Unit and Bethlem Royal Hospital.

Helen O'Connor, GMB membership development officer, said: 'Our members provide vital services to the patients in both NHS trusts and they are sick and tired of the bullying and harassment, having pay held down and staffing cutbacks.

'Outsourced staff get less pay, lower sick pay, fewer holidays and are treated far less favourably than staff directly employed by the NHS.

'We are calling on ISS to get around the table with GMB, the union of choice for these workers and take genuine steps to address our members' grievances. If ISS cannot treat their workforce in a fair way, then we all really need to question whether these contracts are value for money for the public purse.'

In response, a spokesperson for South London and Maudsley NHS Foundation Trust, said: "Our staff are our greatest asset, and we know that staff who feel supported at work provide the best care for our patients and the people who use our services. We want our staff to be able to support themselves and their families and afford the costs of living in London.'

They added: ‘We hope that ISS and GMB can resolve their dispute without the need to take industrial action.'