The SNP Government’s botched Census added £6 million to the cost of compiling essential data, according to a scathing report from Audit Scotland.

Constitution Minister Angus Robertson controversially delayed the Scottish census by a year because of the pandemic, though the English and Welsh surveys went ahead as scheduled.

Only 79% of Scots completed the documents before the end of April deadline, forcing the government to extend it until the end of May.

This boosted the completion rate to 89%, but this was still below the 90% target to ensure the census data could be used to produce the most accurate population statistics.

The census in England, Wales and Northern Ireland was carried out in March 2021 and reported an overall return rate of 97%.

The Auditor General today said that apart from the poor return, delaying the Scottish census by a year meant that costs during this financial year will rise by £6m to £144.6 million.

Stephen Boyle, Auditor General for Scotland, warned the government must find out why the response rate was so low so they do not have to waste as much time and energy again.

He said: “The census is a vital data gathering tool that allows public services to be planned properly. It’s important that National Records of Scotland establishes why the return rate was significantly lower than the other countries in the UK.

“Those lessons should be shared and will be crucial to planning for future censuses and surveys.”

Donald Cameron, Scottish Conservative Shadow Cabinet Secretary for the Constitution, External Affairs and Culture, said: “It was clear from the moment that the Scottish Government decided to hold their census on a different date from the rest of the UK that it would cause trouble.

“Now the Auditor General has confirmed that this led to increased costs and a worse response rate than any other part of the country.

“He’s right that lessons must be learned – and I would hope Angus Robertson has the sense to accept them.

“The first of these is that the SNP must never again allow manufactured differences to distort the proper conduct of government business, wasting public money in the process.”

The Scottish Government, councils and other organisations use census data to help plan services and allocate funding. The Registrar General is responsible for planning and running the census in Scotland.