Kent Police says it will not be investigating concerns about the election expenses run up by the Conservative party during the Rochester and Strood by-election.

Complaints were registered with the force after revelations about expenditure during the campaign suggested the party may have breached the limits set for the constituency. The party said all its expenses were properly declared.

The revelations were reported by Channel 4, which said it had evidence from invoices from hotel costs that were not properly declared in returns to the Electoral Commission.

The Labour candidate Naushabah Khan had registered her concerns with the police as had the then agent for Mark Reckless, Chris Irvine.

In a letter to Kent crime commissioner Ann Barnes, Mr Irvine said: “The level of alleged overspend is such that I feel compelled to request that you consider whether it is appropriate for Kent Police to investigate further whether or not the law relating to election spending in a by-election has been breached as alleged in the Channel 4 investigation.”

Naushabah Khan said she had asked the police for an assurance “that this evidence and matter will be investigated, and if necessary referred to the appropriate authorities to reassure the residents of Rochester and Strood constituency that established electoral laws and procedures, which are designed to protect our democracy have been complied with.”

Kent Police said in a statement: “The spending in the Rochester and Strood election has been raised as an issue over a year after the event and as such it falls outside the time period for investigation. Kent Police officers have taken legal advice in relation to this matter.”

The by-election in November 2014 saw Mark Reckless win the seat only to lose it at the general election.

The Electoral Commission has confirmed that it is to probe similar allegations about expenses incurred by the Conservative party during the election battle in South Thanet.