POLICE Scotland has classed the Liberal Democrats and the Tories as "bad debtors" after the coalition parties refused to pay nearly £1 million in policing costs.

The single force took the drastic move after the parties benefited from a police presence at their conferences but declined to pick up the tab.

SNP MSP Sandra White said the revelation was "hugely embarrassing".

The Home Office pays 85% of the policing costs for party political conferences in England, but not in Scotland as law and order is devolved.

The lack of a separate pot of money north of the Border means Scottish conference policing must be paid for by the parties themselves.

At last year's LibDem gathering in Glasgow, which lasted five days, Nick Clegg's party racked up an £800,000 policing bill.

However, when the LibDems refused to pay, Police Scotland responded by sending a skeletal presence to this year's conference in the same city.

Similarly, the Scottish Conservative Party conference in Edinburgh required a policing presence due to the attendance of Cabinet ministers.

However, a £22,000 bill also went unpaid.

The force has concluded that the debts, which could pay for dozens of police staff and officers, will not be recouped.

Putting the coalition parties on a "bad debtor" list means no police service will be made available to either organisation unless costs are paid up front.

The row is particularly embarrassing for the LibDems, as the Scottish party has campaigned against police cuts.

Scottish leader Willie Rennie has attacked the single force's plan to close control rooms, while their justice spokeswoman has criticised the slashing of police staff jobs.

Quizzed on the row earlier this month, LibDem Treasury Minister Danny Alexander said he was not aware of the facts behind the controversy.

According to the UK party's accounts, the LibDems turned a £511,385 profit on conferences last year.

If the force had received the £800,000 from the LibDems the party would have made a loss.

Police Scotland assistant chief constable Bernard Higgins said: "It was well documented through the planning process with the Home Office, Scottish Government, the Liberal Democrats and Police Scotland that all we hoped to achieve was parity with our colleagues in England and Wales in terms of costs associated with the policing of UK political party conferences. It remains a source of disappointment that this was not the case.

"In terms of the Scottish Conservative Party conference it would be inappropriate for us to comment on previous discussions which are now concluded."

The SNP's White said: "The LibDems being placed on Police Scotland's bad debtor list highlights the fact that they are a complete shambles of a political party.

"It is high time Willie Rennie as the leader of the LibDems faced facts. He must ensure his party pays the bill to Scotland's police immediately. Failure to do so is a failure to support our policemen and women in carrying out the excellent and important job they do."

She added: "And Ruth Davidson needs to sort this out immediately - the officers of Police Scotland do a great job of protecting our streets and communities, and for the Tory Party also to be defaulting on their debts is totally unacceptable."

A spokeswoman for the LibDems said: "In line with ACPOS guidelines, the Home Office absorbs policing costs for party conferences. As policing is devolved it then falls to the Scottish Government to cover these events. Last year, the Scottish Government refused to do this. This is a matter for the Home Office, the Scottish Government and Police Scotland. We have not been sent a bill."

A Scottish Conservative spokesman said: "This is a private matter between the party and Police Scotland."