The culture secretary, Matt Hancock, is considering a government inquiry after a complaint from libraries body Cilip about Northamptonshire’s bitterly protested plan to close almost 60% of the county’s libraries.

Cilip submitted the formal complaint earlier this month, arguing that plans to close 21 libraries and dramatically reduce opening hours would fail the council’s statutory duty to provide a comprehensive library service.

On Tuesday, Hancock told the council’s acting leader Matthew Golby in a letter that he would “consider the complaint fully” and “decide if a local inquiry is needed to resolve any serious doubt or uncertainty as to whether the council is complying with its statutory duty”.

The closures were also slammed by the all-party parliamentary group for libraries, with chair Gill Furniss, MP for Sheffield Brightside, calling on Hancock to “use the full powers at [his] discretion to ensure the residents of Northamptonshire receive the quality of services they are, under statute, entitled to”, and to “intervene and establish a formal inquiry as a matter of urgency”.

According to the group, the council’s plan would leave Northamptonshire with eight large and seven medium branches, leaving one library for every 60,000 residents . The MPs said that the European average was one library per 16,000 people, and “the worst proposals to date – which were not fully implemented – were in Swindon which would have resulted in one library for every 44,000”.

The reductions in opening hours, with some libraries initially due to open for only three hours a week, were introduced after the county council’s spending was cut across the board in February. After widespread protests and criticism, the council subsequently said it would “aim to ensure every library in the county can open at least three days a week … dependent on availability of temporary staff”.

Cilip chief executive Nick Poole welcomed the minister’s decision and called on the council to halt its plans to reduce library services until an inquiry was held.

“Local residents do not deserve to lose valuable public services for good during a period of local political instability ... [Libraries] are trusted spaces at the heart of communities that make a positive difference to people’s health, wealth and well-being,” he said.

Cilip’s complaint includes “the council’s failure to properly consult, an inaccurate Equalities Impact Assessment, failure to act appropriately on financial advice received, and failure to meet their statutory duty to provide a comprehensive and efficient service”.

With other local authorities also warning about their financial sustainability, Furniss warned that Northamptonshire’s financial issues were unlikely to be unique. She joined Cilip’s call on the DCMS to provide a “clear and transparent” definition of what a council’s “comprehensive and efficient” library service should look like.

“Given the lack of library standards in England,” she said, “the absence of a clear definition causes unnecessary confusion amongst local authorities as to the services they should provide and amongst local residents as to the services they should receive.”

In his letter to Golby, Hancock said that there was no set timetable for considering the complaint and would be determined by the complexity of the issues to be addressed.