A computer programming error may have caused an exams blunder affecting 1,000 candidates in Scotland, it has emerged.

The body which processes university applications has written to the affected students apologising for the mistake.

The Universities and Colleges Admissions Service (Ucas) said it now believes a glitch got into the system when it reprogrammed its computers ahead of this year's results.

We are now in a position to conduct an inquiry to ascertain exactly what happened

Tony Higgins Ucas chief executive

The error came to light on Tuesday as Scottish pupils saw their exam results successfully delivered by the Scottish Qualifications Authority.

However, about 1,000 students who narrowly failed Higher or Advanced Higher exams were given better grades than they had actually earned.

The incorrect data was then sent to universities and colleges so they could decide which candidates to reject or accept.

Ucas sent out the corrected data on Tuesday night.

Three Scottish universities have confirmed that they will honour all the places offered in error.

However, other institutions say they are considering applications on a case-by-case basis.

Correct information

Ucas has also written a letter of apology to those who received letters based on incorrect results.

"The clearing process in Scotland has not been affected and clearing will begin as scheduled in the rest of the UK from tomorrow," said chief executive Tony Higgins on Wednesday.

"Our first priority was to take action to ensure that SQA candidates and universities and colleges had accurate and correct information.

Some universities will honour offers of places

"We are now in a position to conduct an inquiry to ascertain exactly what happened."

The organisation rewrites and updates its computer software every year to take account of changes in exams.

Initial inquiries have suggested that the problem got into the system at that stage.

Mr Higgins added: "This computer and its predecessors have been running since 1962 and this is the first glitch we have had in all that time.

"They were thoroughly checked and that's why we are a bit bewildered as to exactly how it happened.

The appropriate action was taken and I kept very much on top of that

Cathy Jamieson Education Minister

"But we will find out and report on that."

Scottish National Party education spokesman Mike Russell said he would be asking senior staff at Ucas to tell the Scottish Parliament's education committee what went wrong.

He also criticised Education Minister Cathy Jamieson for not doing enough to address the problems.

However, on Wednesday she said: "I was very conscious that if the error was not rectified then Scottish students could be put at risk because the English A level results are due out tomorrow.

"So the appropriate action was taken and I kept very much on top of that - and indeed am still doing so."