The head of a trade union branch has blasted public sector workers who chose not to strike on Wednesday and branded them “scabs”.

Jon Rogers, head of Lambeth Unison, condemned those who went to work during the national walkout as “immoral and unacceptable”, adding that they should be “ashamed” of their decision.

In an 800 word email to his colleagues, he said those who crossed the picket line were “scabs” and had committed “one of the worst things that can be done”.

He said: “To the small minority of UNISON members who refused to respect the democratic decision to strike, and went in to work, I say two things.

“First, you were wrong. What you did was immoral and unacceptable and you should be ashamed. Whatever reason you thought you had to let your colleagues down it was not a good reason.

“It will (if you are a decent person) be difficult for you to look into the eyes of colleagues who gave up a day’s pay to defend our pensions, knowing that you were prepared to let them make that sacrifice for you.

“It may be unpleasant to be called a “scab” but it is more unpleasant for those of us who take strike action to know that there are a minority who refuse to accept democratic decisions.

“If you cross a picket line you are a scab. There is no other word for it and it is one of the worst things that can be done.

“Secondly, there is still hope for you. Should further strike action be necessary (as I fear and expect) then you will have an opportunity to redeem yourself by taking the right decision next time. Please think carefully about this and never again make the mistake of crossing a picket line.”

The email, which was leaked to Sky News, has prompted outrage from Prime Minister David Cameron and Conservative Party co-chairman Baroness Warsi.

About 500 protesters marched through Windrush Square in Brixton on Wednesday. Some 76 per cent of schools in Lambeth were also closed and a further 17 per cent partially closed, along with all of the borough’s libraries.

Unions said the walkout, which saw up to two million people protesting across the UK, was the biggest national strike since the 1979 Winter of Discontent.

Mr Rogers declined to comment on the email, but a UNISON spokesperson said he had apologised for his actions and that his message had since been withdrawn.

She said: “The email has been withdrawn. The branch secretary was acting independently. He has confirmed that it was sent after a long tiring day and he regrets it being sent. He apologises for any offence caused.”