UK Government ministers were challenged after photos apparently showing unpublished papers on controversial plans for a post-Brexit internal trade market appeared on social media.

Scottish Constitution Secretary Mike Russell said he raised the issue after a picture on Twitter appeared to show a press release concerning the UK Government’s Internal Market Bill.

Jenny Gilruth, the Europe minister for the Scottish Government, had noticed the tweet by Political Pictures, and alerted him to it, he said.

Mr Russell said it “broke in the last few minutes” of the Joint Ministerial Council meeting on EU Negotiations – which brings together UK Government ministers and their counterparts from Scotland, Wales and Northern Ireland.

He added: “I was able to raise it given that devolved administrations had just been asking (with no success) to see the bill.”

Mr Russell said instead of asking to see the proposed legislation – for which he has already vowed to fight “tooth and nail” – he should “just have ambled past Dover House”, where the Scotland Office has its London office.

The Scottish Government has already spoken out strongly against the UK Government’s plans for an Internal Market Bill, branding the move a Westminster “power grab”.

In contrast, Cabinet Office Minister Michael Gove has insisted the proposed legislation, which will set out arrangements between the four nations of the UK after the Brexit transition period comes to an end, will result in a “power surge” for Holyrood.

However, SNP Westminster leader Ian Blackford said: “The leaked pictures confirm what we have been warning about since these proposals first emerged – the Tories are preparing to overrule the democratic will of the Scottish Parliament and are laying the groundwork for the biggest raid on devolution since 1999.”

He added: “Despite the decisive rejection from the Scottish Parliament – the Tories are intent on undermining devolution and continuing with their power grab plans.

“The SNP remain firmly opposed to this power grab and the Tory government must step back from these plans that will take a wrecking ball to the very foundations of the devolution settlement.”

Meanwhile, Scottish Green co-leader Patrick Harvie said: “The Tories’ internal market proposal was subject to a very short consultation, with no draft bill presented, and which took place while the Scottish Parliament was in recess.

“Now just three weeks after the consultation closed it seems ministers are already singing off the press release, but still nobody has seen the legislation.”

The Green MSP added: “The proposals are completely incompatible with devolution, threatening a huge range of policy areas including environmental, food and farming standards.

“If allowed to proceed these plans would even threaten Scotland’s decisions to ban fracking or prevent new nuclear power stations. The internal market could also put at risk bold public health measures such as minimum unit pricing, and it certainly could allow further private sector involvement in our NHS.”

He hit out: “The UK Government has taken its contempt for Scotland to new levels during this process. It has refused to discuss this assault on devolution with MSPs and it has declined to show the draft legislation to devolved administrations.”

A UK Government spokesman said: “We’ve been clear that we will be legislating to protect the UK’s vital internal market when the Transition Period ends.

“This will protect trade and jobs and ensure that goods can continue to travel barrier-free throughout the UK, as has been the case for hundreds of years.

“Following our consultation, we are now preparing this legislation. Further details will be confirmed in due course.”