DELAYING the census deadline has cost Scottish taxpayers about £6 million, Constitution Secretary Angus Robertson has said.

Additional costs were lower than expected, with the Robertson previously suggesting it could amount to £9.76m, taking the total cost to £148m.

Some 87.9% of households have returned the once-in-a-decade form to the National Records of Scotland (NRS) – with just 10 local authorities surpassing a 90% response rate.

The census collection ended on May 31 – almost a month later than planned – after hundreds of thousands of homes failed to return the digital-first document.

Liberal Democrat MSP Willie Rennie told Robertson the £6m figure is a “huge sum” wasted.

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He said: “I’m not sure the minister should be making a virtue about only spending an additional £6m on this survey and census extension.

“It’s still a huge sum of money that he shouldn’t be wasting.”

The forecasted sum equates to 4.3% of the total 2022 census costs, Robertson said.

A data collection exercise undertaken in the final week of the census revealed that 35% of households did not return the census because they “were too busy”.

A further 17% said they were unaware of the census, while 14% did not know it was a legal requirement to complete.

Some 5% refused over concerns about privacy, government trust, the nature of questions and access to paper copies, Robertson told MSPs in a ministerial statement on Thursday.

He said: “It’s clear the need for an extension and the fact that unfortunately there remains a portion of Scotland’s households who have not completed the census.

“That is despite a large-scale public awareness campaign, millions of letters and more than 1.68 million field visits.

“It’s important that we understand why this happened so that lessons can be learned for the future of the census.”

Those who have failed to return the census could face prosecution, the minister said.

The total number of non-responding households was 316,000, while almost 2.3 million completed the census.

He said: “Filling in the census is a personal, legal responsibility and allowing people who have previously refused to respond a window to do so is standard procedure.

“In line with previous censuses, anyone who has directly refused to fill in the census has now been written to and given a final opportunity to do so before NRS begin the process of referring them for potential prosecution.”

Earlier, Scottish Conservative constitution spokesperson Donald Campbell asked Robertson if the census was a success given it did not meet the NRS target of 94% completion.

Robertson said he believes the response was at a “good level” and said he would “totally and utterly repudiate assertions of writing off anything in the census”.