The Health Scrutiny Panel for Lincolnshire made the decision after it said no progress had been made following a referral of the decision to the Secretary of State in January 2018.
United Lincolnshire Hospitals Trust closed the department overnight in August 2016, a move which it said was “temporary”.
Councillor Carl Macey, chair of the panel, said it was “unacceptable” that the service has been closed overnight for two and a half years.
“We felt we were in a position today to elevate this matter as high as we could,” he said.
“Our hope is to return services in Grantham to overnight,
“At the moment in time residents have had 30 months without any overnight services and we do not think that is acceptable.”
Since the closure, the committee has referred the matter to the Secretary of State in January 2018 on the grounds of “inadequate consultation”.
The Minister for Health at the time, Steve Barclay MP, intervened in the matter the following September asking for an update from the trust and South West Lincolnshire CCG on the closure.
Both organisations confirmed that a report had been handed to the Department for Health and that publishing the document was a matter for the minister.
But the panel said that no report has been made public or given to the committee by ministers.
Councillor Macey said the committee hoped the referral to the Prime Minister will provide an outcome for the residents of Grantham.
Campaigners have called for a solution to the ongoing overnight closure after increased demand at the department.
Bosses at ULHT have maintained that the future of Grantham A&E is being developed by the Lincolnshire STP and will form part of a public consultation.