Nicola Sturgeon has defended her government’s under-fire deposit return scheme (DRS) despite small businesses shunning signing up to the policy before Tuesday’s initial deadline.

The Scottish Government has extended the deadline to allow producers to register.

The move came after Circular Economy Minister Lorna Slater admitted that only 664 businesses had registered with Circularity Scotland.

In December, Ms Slater told MSPs that around 4,500 producers would be involved.

But speaking at First Minister’s Questions, Ms Sturgeon claimed that the number was closer to 2,000 with multiple businesses registering under one account.

Scottish Conservative leader Douglas Ross said: “At midnight on Tuesday, businesses in Scotland were legally required to sign up to the SNP-Greens’ deposit return scheme.

“Thousands of producers rightly decided not to because the scheme is an absolute shambles.

Read more: Thousands of drink producers shun 'disaster' deposit return scheme

“Lorna Slater, the minister in charge, said just 664 businesses had registered but refused six times in this chamber yesterday to say, how many should have signed up.

“So will the First Minister give us that answer now – how many businesses should have signed up to her government’s deposit return scheme?”

But Ms Sturgeon insisted that “when a big change is introduced”, it is” understandable there will be concerns about it”.

She added: “I have deep respect for the concerns that are being raised by businesses. Government will continue to work with business to address those.”

The First Minister hit out at the “sheer opportunism of some opposition parties”, who she said had supported the scheme but “now indulge in knee-jerk opposition”.

Read more: Douglas Ross apologises for 'industrial language' during FMQs

She said: “The number of companies in the drinks industry inevitably changes over time.

“At the outset of introducing this scheme, it was estimated that there were around 4,500 companies.

"However, significantly less than that will have to register because once groups of companies registering under one registration are identified, the estimated number of induvial producers, importers, will be below 2,000.”

Ms Sturgeon said that the number of companies registered is “not actually the most relevant statistic”.

She added: “The most relevant statistic is the share of the market, the percentage of products that are included. That is over 90 per cent are now included in this scheme.”

But in response, Mr Ross told the FM that “when you’re in a hole, stop digging”.

He pointed to Ms Slater being “absolutely unable to answer a basic question yesterday” over how many producers have not signed up, adding it is “one that is so important”.

Mr Ross said: “Businesses are giving this government a very clear message loud and clear – their deposit return scheme is a complete disaster.

Read more: Kate Forbes: SNP must stop anti-business attitude amid DRS 'carnage'

“The Scottish Wholesale Association said it could be a car crash, UK Hospitality Scotland say it is flawed. Innis and Gunn say it’s unworkable. The Scottish Chambers of Commerce, last night after listening to the minister, said business concerns have been completely ignored.

“Even at this late stage, will you finally just once listen to Scottish businesses and pause this scheme.”

But the First Minister stressed that “the vast majority of products are actually produced by a relatively small number of producers”.

She added: “We will continue as we have done. There have already been a range of concerns that have been responded to.

“We will continue to liaise with business sensibly and responsibly.”