Council tax collection rates have been criticised by the Tories

But the Accounts Commission report said that �600m of council tax had been outstanding since 1996.

Local authorities collected 92% of the tax last year, but rates varied from 98% in Orkney to 85% in Glasgow.

The Tories criticised the performance and the finance minister said he wanted to see improvements - but councils said they were doing all they could.

The Accounts Commission report said that only eight of Scotland's 32 councils met targets from the Department of Work and Pensions for dealing with benefit claims last year.

'Unreliable data'

However, the time taken to process claims fell from 49 days to 47 days.

Dundee City Council was excluded from this and another category because it produced what the Accounts Commission described as "unreliable data".

The report found an improvement in the time taken to pay invoices, with Dundee, Aberdeen, Perth and Kinross and West Lothian councils paying at least 90% on time.

Accounts Commission chief Alastair MacNish said: "Over the past 12 months, councils have improved in a number of key areas in line with the government's efficiency agenda.

I have made it clear on a number of occasions that I want to see further improvement in this area Tom McCabe Finance Minister

"The reduction in time taken for councils to process benefit claims and pay invoices, along with the increase in council tax collection levels for the fifth consecutive, year is encouraging."

However, Tory spokesman Brian Monteith said: "If the Scottish councils improved their collection rate even to that in England, over �50 could be cut from the average band D household.

"I am sure the people of Scotland will be rightly wondering why it is that their tax bill is 5% higher than it should be."

Finance Minister Tom McCabe said: "I have made it clear on a number of occasions that I want to see further improvement in this area.

"The poorest performing councils lag well behind the rest and I urge those authorities with lower collections levels to seek advice from some of the better performing councils.

Genuine hardship

"There is simply no excuse for councils not to take all practical steps to collect unpaid council tax or community charge debts."

However, John Pentland of the Convention of Scottish Local Authorities (Cosla) said that councils were "doing everything they can to make sure people pay and pay on time".

Cosla's finance spokesman said: "Councils have some sympathy for those who face genuine hardship and who face the dilemma of paying either a heating bill or a council tax bill.