A 48-hour strike began at 7am at Blackpool Victoria, Clifton and Fleetwood hospitals.

Unison says staff are angry that the trust is refusing to compensate them fairly for work carried out when they were on the wrong grade. The workers had been carrying out tasks – such as taking blood, performing electrocardiogram tests and inserting cannulas – that should have been paid at a higher hourly rate.

The trust has now accepted that the healthcare assistants were performing extra duties above their role and will provide them with back pay. However, the union says senior managers are trying to withhold some of the money owed to staff, even though NHS policy says nobody should be worse off as a result of a promotion.

Unison North West regional manager Dan Smith said: ‘It's outrageous the trust is refusing to pay staff properly for all the extra work they've done.

‘Healthcare assistants have been working above their pay grade for years, in some cases decades. It's only right they're fairly compensated.'

In response, Maggie Oldham, chief executive at Blackpool Teaching Hospitals, said: ‘It's very disappointing that strike action has been confirmed by Unison, especially as we have agreed to increase and backdate pay for eligible health care assistants (HCAs), in line with NHS terms and conditions.

‘It is telling that the Royal College of Nursing has responded positively and is putting the deal to its members.

‘What Unison has asked for is outside of standard NHS terms and would leave our trust with a multi-million-pound bill it cannot pay.

‘We value our HCAs, they play a vital role in the care we provide, but we cannot agree to these unreasonable demands.'