The workers - predominantly as cleaners and caterers - are protesting against 'their treatment at the hands of their employer, including frequently incorrect pay, as well as being overworked, under-appreciated and not respected'.

Helen O'Connor, GMB regional organiser, said: ‘Without these members, the hospital would simply not be able to function, but these GMB members are treated so poorly. Their workloads are so unsustainably high that the members are reaching crisis point, which will obviously be affecting service provision.

‘Patients need to be fed, wards need to be cleaned and yet Mitie can't even be bothered to pay them their wages on time.

‘Our members will be demonstrating in numbers tomorrow lunchtime to try and send a clear message to Mitie and to Trust management – just because they aren't directly employed doesn't mean they aren't NHS workers and it certainly doesn't mean you can muck about with their pay and treat them worse than NHS staff.'

In response, a Mitie spokesperson, said: ‘Our teams provide valuable services to support our NHS and we are proud of the work our colleagues do every day at St George's. It is disappointing that GMB has decided to arrange this protest without engaging with us. 

‘If we are alerted to issues regarding workloads or pay, we work quickly to resolve these. We are not aware of any outstanding issues.'