A new proposed definition of Islamophobia could undermine counter-terrorism laws, one of the UK’s most senior police officers has warned.

Martin Hewitt, chairman of the National Police Chiefs’ Council, said the term under consideration could cause confusion among officers and hamper the fight against terrorism.

The definition proposed by the All-Party Parliamentary Group (APPG) on British Muslims is: “Islamophobia is rooted in racism and is a type of racism that targets expressions of Muslimness or perceived Muslimness.”

Its report on the definition said it had been reached after “widespread consultation with academics, lawyers, local and nationally elected officials, Muslim organisations, activists, campaigners and local Muslim communities”.

Mr Hewitt said: “We take all reports of hate crime very seriously and will investigate them thoroughly, however we have some concerns about the proposed definition of ‘Islamophobia’ made by the All-Party Parliamentary Group on British Muslims.

“We are concerned that the definition is too broad as currently drafted, could cause confusion for officers enforcing it, and could be used to challenge legitimate free speech on the historical or theological actions of Islamic states.

“There is also a risk it could also undermine counter-terrorism powers, which seek to tackle extremism or prevent terrorism.

“It is important that any definition of anti-Muslim hostility is widely consulted on and has support across the Muslim community.”

Baroness Warsi, treasurer of the APPG, called the terrorism claim “extraordinary and disturbing” and said the definition does not seek to stop criticism of Islam.

The Times newspaper published a leaked letter that Mr Hewitt wrote to the Prime Minister raising his concerns.

Baroness Warsi said on Twitter that she had written to Cabinet Secretary Mark Sedwill about the leak because “the issues involve national security”.

The Prime Minister’s official spokesman declined to comment on the letter but said: “Any hatred directed against British Muslims and others because of their faith or heritage is completely unacceptable.

“We are conscious that the APPG’s proposed definition has not been broadly accepted, unlike the International Holocaust Remembrance Alliance definition of anti-Semitism before it, which was adopted by the UK Government and other international organisations and governments.

“This is a matter that will need further careful consideration.”

Shadow minister for women and equalities Naz Shah said if the Prime Minister rejects the definition, “the message she sends to the Muslim community will be heard loud and clear”.

She went on: “It has been a great struggle to get the police to record Islamophobia as a specific crime, so it is deeply worrying to see the National Police Chiefs’ Council bringing terrorism into the discussion about tackling Islamophobia.

“This shows a worrying trend of seeing British Muslims through the lens of terror and security, and the Prime Minister must distance herself from this immediately.”

But National Secular Society chief executive Stephen Evans called the definition “vague and unworkable”.

He said: “If the Government adopts this definition it will restrict important discussion and debate and, as the criticism of senior officers shows, undermine the police’s ability to keep people safe.

“We urge the Government and public bodies not to join the rush to adopt this definition. We must resist the urge to respond to anti-Muslim bigotry by going along with the censorious whims of some ‘Muslim community leaders’, chilling free expression and undermining social cohesion.”