Hampshire County Council has joined 15 other local authorities in warning Sir Keir Starmer that the merger of councils in the county could put services for vulnerable residents at risk.

In a letter to the prime minister, council leaders criticised ministers’ approach to creating new unitary councils, arguing that recent decisions departed from the government’s own criteria and risked undermining frontline services, including adult social care and children’s services.

The intervention comes after the government announced plans for 15 new unitary councils across Essex, Suffolk, Norfolk and Hampshire as part of its local government reorganisation programme.

In Hampshire, the county council proposed a three-unitary model alongside the Isle of Wight. However, ministers opted for four new councils instead, a decision county leaders say raises serious questions about how proposals were assessed.

The letter, coordinated by the County Councils Network (CCN), was signed by 16 county councils across England and calls on the government to reconsider aspects of the reorganisation programme.

Council leaders argue that the pace and scale of the reforms risk diverting attention and resources away from frontline services at a time when demand for social care continues to rise.

They also claim the decisions announced in March were inconsistent with the government’s statutory criteria and had “all the hallmarks of a set of short-term political choices”.

Hampshire County Council leader Cllr Nick Adams-King said the Government’s approach posed a “serious risk” to Hampshire residents.

The Conservative leader said: “This is not about resisting reform. Local government can and should be improved. But reform must be evidence-led, financially sound and designed around communities — not rushed through to suit short-term political priorities.

“In Hampshire, the government has chosen the most radical option: abolishing the county and district councils and replacing them with four new unitary authorities, including boundary changes that split long-standing communities.”

He added: “My concern is clear. If councils are made too small, too fragmented and too weak financially, residents will pay the price — particularly those who rely on adult social care, children’s services and SEND support.

“That is why we are calling on the Government to publish the evidence behind its decisions, engage properly with councils, and stop pressing ahead at pace with proposals that appear increasingly inconsistent and politically driven.

“Hampshire needs reform that strengthens services, protects communities and is financially sustainable for the long term. It does not need a rushed reorganisation that risks costing more, delivering less and leaving vulnerable residents exposed.”

The CCN also said the government’s preferred options in Hampshire, Essex and Suffolk represented the “most radical” proposals under consideration and would involve complex boundary changes and the break-up of existing county-wide services.

During the local election campaign, Cllr Adams-King pledged that, if re-elected as council leader, he would pursue legal action if ministers failed to provide what the authority considers a satisfactory explanation for rejecting local proposals and selecting an alternative structure for Hampshire.

Following the elections and a vote at County Hall on May 21, Cllr Adams-King was re-elected as council leader and confirmed that the authority would pursue a judicial review.

At the time, he said: “I confirm today that this administration will move immediately to pursue a judicial review of the local government reorganisation outcome.”

However, cabinet members are due to meet on Tuesday, June 9, to consider further legal advice.

Should that advice indicate there is an arguable case, members will be asked to decide whether to star legal proceedings to challenge the Secretary of State’s decision.