Some operations are not taking place within the nine-month guarantee

The SNP has obtained figures which suggest a large rise in the number of people being taken off the official waiting list in certain specialities.

The Scottish Executive said that NHS boards were expected to follow strict guidelines.

The executive has promised that no patient should wait more than nine months for an operation.

We require some explanation and we've had none so far Shona Robison SNP health spokeswoman

However, people are given an Availability Status Code, or ASC, when they cannot attend an appointment for personal, social or medical reasons.

That means hospitals do not have to abide by the nine-month guarantee.

Of the 35,471 people reported by the executive to be in this position in the first quarter of 2005, nearly 17,500 were waiting more than nine months for treatment.

New figures obtained by the SNP show that the number of children being given the code because their operation was of low priority rose from one in June 2003 to 249 in March this year.

Inquiry call

The number of cardiac patients who had apparently delayed their operation for personal reasons doubled.

The number of patients requiring orthopaedic or trauma surgery who had some kind of medical constraint increased by 1,000.

SNP health spokeswoman Shona Robison called for the executive to explain the figures.

NHS boards follow guidelines on managing waiting lists

Speaking on BBC Radio's Good Morning Scotland programme, she said: "Many of these people won't even know they've lost their waiting time guarantee.

"All they will know is that they're waiting a long time for treatment."

However, she added: "Why has there been such an increase? What has changed in the last two years that has led to such an increase?

"Either it's a change of policy or a change of practice and we need to know what that is because it isn't fair.

"We require some explanation and we've had none so far.

"The executive should be launching an inquiry into this and looking at the practices of health boards to see whether people are being put on these hidden waiting lists who shouldn't be."

We really have to stop this smear that we are somehow using this as some kind of wheeze to hide figures Margaret Curran Parliament Minister

Parliament Minister Margaret Curran said she "felt frustrated" with the SNP's efforts to find fault with waiting lists.

She said Audit Scotland had already concluded the figures had not been manipulated in any way.

"We really have to stop this smear that we are somehow using this as some kind of wheeze to hide figures," the minister added.

System improvements

"We recognise there need to be improvements in the system, ensure people get proper time for appointments and that they are properly dealt with by the NHS.

"The NHS is a big, complicated organisation. But it's frustrating to be criticised for things you have recognised in the past and are actively changing."

The executive was in regular contact with health boards throughout the country and there would be different reasons for varying waiting list figures, Ms Curran added.

She said health boards were "abundantly clear" on the guidelines they had to adhere to over the management of waiting lists.

Ministers plan to abolish the ASC system in 2007.