The 37 phlebotomists at the two hospitals launched action in March after Gloucestershire Hospitals NHS Foundation Trust refused to regrade staff who had been performing extra duties at work.

Unison general secretary Christina McAnea said: ‘It's a scandal that hospital managers have allowed this dispute to drag on for 200 days. They must pay up now and show the phlebotomists the respect they deserve for the skilled work they do.

‘These dedicated NHS staff help diagnose illnesses and keep services running smoothly. They didn't want to strike but were left with no choice after years of being underpaid and ignored.'

Unison said the dispute could end immediately if the trust agreed to pay staff the additional £1.09 per hour that would take them to the correct pay band.

A Gloucestershire Hospitals NHS Foundation Trust spokesperson said: ‘Constructive negotiations have taken place and continue with the hope of reaching a resolution.'