The parking charge notice, addressed to Devon and Cornwall Police, requires the force to pay £85 within 28 days.

It refers to a car parked in a Plymouth car park at midnight on 2 November.

Police vehicles are exempt from fines when performing operational duties, but officers in Plymouth were told by the parking firm they had to follow the "appeal process" to contest the ticket.

Some officers tweeted their frustration after they explained the situation to the company, which said the force would need to submit a written appeal.

The letter goes on to say the charge will be reduced to £50 if paid within 14 days.

The police vehicle was left in the car park between 23:55 and 00:29 GMT without a valid Pay by Phone transaction, according to the notice.

'Appeals process'

Police confirmed the ticket was issued to a "fully marked police car" responding to an incident at a pub in the city.

They said their vehicles are exempt from parking fines while performing "operational duties".

Officers said they contacted the company responsible to request the ticket be scrapped and were told the "appeals process must be followed".

"It is fair to say that officers would rather be spending their time responding to 999 calls than dealing with an appeal for a parking ticket," they added.

Officers at the Plymouth Response A Section tweeted the company should "please hold calling 999" while they fill out their written appeal.