Boris Johnson’s former senior adviser Dominic Cummings has threatened to reveal a “crucial” Covid document ahead of an appearance next week at a Commons committee investigating the government’s handling of the pandemic.

It comes after Mr Cummings took another public swipe at the government, accusing ministers of pursuing a “joke” borders policy as questions mount over the action taken to prevent the spread of a new strain first identified in India.

Posting on his social media account, Mr Cummings, who left No 10 at the end of 2020, said he was in possession of the “only copy of a crucial historical document from Covid-decision making” and asked followers how to release it.

Providing multiple options, the former No 10 aide suggested giving it the joint health and science committee, which is holding an inquiry into the response to the crisis, or posting a blog on his personal website he last month used to suggest the prime minister lacked “competence and integrity”.

Mr Cummings also suggested he could sell the document as a non-fungible token, or NFT, through an online auction. He could give the cryptocurrency proceeds to a “Covid families charity”, he suggested.

However, a few moments later, he said: “Did 1st Twitter poll, botched options like idiot so scrapped… my point as well as giving to [committee] I [could] also raise £ for a charity — not instead of — but I botched it… Obviously I’ll give to [committee] on Wed.”

In a separate post on Tuesday, he claimed that vaccines could have been in use earlier in the pandemic if greater risks were taken — though the Medicines and Healthcare products regulatory Agency (MHRA) is responsible for examining the safety of jabs.

Mr Cummings said success in the vaccine rollout had “blinded” Westminster to important questions about what could have been done better and how the government will respond to variants.

Writing on Twitter he said “I think we’ll conclude” that human challenge trials – where volunteers are deliberately infected – should have begun immediately which could have meant “jabs in arms summer”.

Mr Cummings also stressed that “one of the most fundamental & unarguable lessons” of February-March 2020 is that “secrecy contributed greatly to the catastrophe”.

“Openness to scrutiny [would] have exposed (government) errors weeks earlier than happened,” he said, questioning why MPs were now accepting “the lack of a public plan now” for the vaccine taskforce to respond to variants.