More than 5,000 civil service jobs are set to go at the Ministry of Defence in a drive to cut costs, prompting alarm among trade unions.

David Williams, the permanent secretary, said the department was aiming to lose 10% of its 56,800 staff by the end of the parliament. It has already shed thousands under the previous government through a hiring freeze that was due to end in March 2025.

Williams revealed the target at a defence committee hearing. It comes after John Healey, the defence secretary, said on Wednesday that he would be making cuts to equipment to save £500m.

Two former Royal Navy flagships, a frigate and two support tankers will be decommissioned, with the savings reinvested into the defence budget. Healey blamed the move on a “dire inheritance” left by the previous Tory administration.

Williams’s comments about reducing the size of the MoD appears to have come as a surprise to those working in the department and the leading civil service trade union.

Fran Heathcote, the general secretary of the Public and Commercial Services union, said: “We had been given no warning this was coming. To announce job cuts in parliament and talk about 10% of MoD jobs being lost as a ‘jumping-off point’ is hugely disrespectful to our hard-working members, who deserve better from their employer.

“Our members in the MoD are doing essential work in keeping the country running and we shall not let them, or other dedicated public servants, pay the price for the previous government’s financial black hole.

“We demand an urgent meeting with ministers to get to the bottom of what is happening at the MoD but, rest assured, PCS will fight for every job because we believe our members’ commitment should be recognised and rewarded, not dismissed in the Houses of Parliament.”

Healey had said the decisions on equipment, before the strategic defence review (SDR) next year, would mean Williams would “lead a leaner department, with more policy muscle and influence”.

Pressed by MPs, Williams said having fewer civil servants would be a significant part of the picture.

He said: “In order to create the headroom for permanent recruitment, where currently we’re relying on professional services or to create headroom for civilianisation, we actually need to take some of the core roles down further to build back up. But I think, as a minimum, a 10% reduction over the lifetime of this parliament is a good jumping-off point.”

He said there were currently “no plans for specific redundancy programmes”, but added: “We’ll look at the balance between inflow, retraining and outflow … But I think that’s something we’ll want to keep under review as the recommendations from the SDR come forward.”