Following a two-day judicial review hearing in the High Court in April, Mr Justice Sales ruled today (10 May) that the previous government acted unlawfully when it introduced, without PCS’s agreement, a new redundancy scheme reducing the rights staff had accrued over time.

In what is a dramatic win for the union’s 270,000 public sector members, the judgement quashes a revised scheme that the government had sought to impose from 1 April. It means the next government, when it is established, must reopen negotiations with the union if it is to agree a new arrangement that protects existing members’ rights.

The union has always maintained the changes to the civil service compensation scheme, which governs payments in the event of redundancy and early retirement, would have made it easier and cheaper to cut tens of thousands of civil service jobs and privatise more of our public services. It has also argued consistently that the government had no authority to act independently.

When PCS members took three days of strike action in March, including on budget day, Gus O’Donnell described it as “misguided” and Tessa Jowell, then the civil service minister said the “time for talking is over”.

Despite widespread anger among the government’s workforce, and opposition from 176 MPs including 121 Labour backbenchers, changes aimed at saving £500 million over three years were forced through. If they had been allowed to stand they would in many cases have robbed civil servants of thousands of pounds if they were forced out of their job.

Strike action was suspended during the election – though the union continued to campaign in targeted constituencies across the UK – but PCS now says a failure to comply with the ruling would risk angering civil servants still further, leading to the possibility of more industrial action.

PCS general secretary Mark Serwotka said: “Our members in the civil and public services refused to sit back and watch their terms and conditions being ripped up in front of their eyes. This ruling is a huge tribute to them for mounting one of the most impressive campaigns this union has seen, in the face of some disgraceful criticism from their employer and ministers.

“We have always accepted that changes are necessary but all we ever asked is that they were fair and protected those who have given loyal service. We will now be knocking on the door of the next government to remind ministers they are legally obliged to reach an agreement with us. If they do not meet their obligations, the union will have to consider further industrial and legal action.”

Hugh Lanning, PCS deputy general secretary, called on the next government to comply with the judgement and enter into talks as a matter of urgency to reach a fair agreement for all civil servants, adding: “This is a major victory for our members, who were being deprived of their rights by a government that refused to talk and reach agreement. Let’s hope the new government obeys the law.”

Richard Arthur, head of trade union law at Thompsons Solicitors, said: “The law says that the government can’t change redundancy rights which have already accrued for civil servants unless the unions agree. As the judge said, this was unsurprising in the circumstances of civil service employment. PCS did not agree to the new scheme and so it was found to be unlawful.”