The human rights joint committee said the government had not made the case for imposing caps on payments under the civil service redundancy scheme, which governs the terms available to civil servants who are made redundant either by compulsion or agreement.

The committee has scrutinised the superannuation bill which is currently going through parliament and is scheduled to have its report stage in the House of Lords tomorrow.

Its findings support the union’s case that because civil servants have accrued a right to certain redundancy terms through their length of service, this is classed as a “possession” for the purposes of human rights law, and should not be “interfered with” unless there is an over-riding public interest.

The committee says the government has failed to explain the justification for applying arbitrary caps that would severely limit payments.

Read the human rights committee's report

Find out how minister reneged on pledge

Read a timeline of the negotiations

The previous government’s attempt to impose a new redundancy scheme was struck down by the High Court earlier this year following a successful judicial review taken by the union.

Last week PCS accused Cabinet Office minister Francis Maude of misleading MPs when he claimed in parliament that the union had declined invitations to negotiate. In fact, the government has refused an offer to meet to discuss an alternative proposal for reform of the compensation scheme.

PCS general secretary Mark Serwotka said: “Every time this or the previous government’s plans to cut civil service redundancy pay have been tested against legislation, they have been found to be unlawful.

“As by far the largest civil service union, we are committed to opposing these cuts, and we say again to the government that it’s time to stop attacking its own workforce and talk to us about agreeing a fair scheme that protects people’s rights.”