British Gas engineers will launch a fresh wave of strikes on Friday in a deadlocked dispute over pay and conditions.

Members of the GMB will walk out for four days, with the union claiming they face being sacked next week if they have not accepted new terms and conditions.

The industrial action will take the number of strikes to 42 since the dispute flared earlier this year.

The GMB said the company will give formal notice of termination next week for staff who have not accepted the changes.

National officer Justin Bowden warned of further strikes and other “appropriate action” if the row remains unresolved.

He said mass sackings were illogical and will leave everyone “bewildered”.

A British Gas spokesman said: “We must change to protect 20,000 UK jobs. There is a job for everyone at the end of this process and our new terms are fair and very competitive.

“Our gas service engineers are some of the best paid in the sector, earning £40,000 and we’ve protected base salaries and pensions from the outset. We’ve made sure colleagues have the information they need to make a choice.

“We know change difficult but we have a responsibility to reverse our decline which has seen us lose over three million customers, cut over 15,000 jobs and seen profits halved over the last 10 years.”

British Gas added it had been clear that new terms will come into place from April 1, but said dismissal would remain a “last resort”.