"STOP being so scared” – Nicola Sturgeon threw out a direct challenge to “scaredy cat” Boris Johnson on Tuesday, telling him she will take him on “any time, any place”.

The SNP leader spoke out from the campaign trail after the Tory leader said he’d never face her head-to-head – because she’s not running to become prime minister.

In an interview with a newspaper, Johnson said it would not be “appropriate” to debate with someone who could not become PM, saying: “Once Nicola Sturgeon takes leadership of a party in Parliament and is a serious contender to be prime minister of the UK, that would be the appropriate moment.”

Responding on social media, Sturgeon referred to Johnson’s claim that he would rather “die in a ditch” than ask Brussels for a Brexit extension prior to actually doing so in late October. Sharing a laughing face emoji, she tweeted: “Is this the ‘die in a ditch’ definition of ‘never’?”

And, speaking on the campaign trail in Stirling, she said she’d already made an in-person offer to face him over Scottish independence, saying: “I remember when he came to Bute House in the summer and was getting into a debate about independence with me. Privately, I suggested to him then that we should take it to the public sphere and have a debate in public about that.

“He seemed to be up for that at the time so I can’t really throw any light on what has changed his mind.”

Adding that Johnson “seems to be a big scaredy cat”, she went on: “If you want to be prime minster, as he is standing in this election to be, then he shouldn’t be running scared from debate and I think it speaks volumes that he is so frightened of debating anybody other than Jeremy Corbyn.

“But I’ll put down a challenge to him right now – I’ll debate him any time, any place. So come on Boris, stop being so scared.”

The comments came hours after Johnson ally Alister Jack, the Scotland Secretary, insisted the Conservative head is not “running scared”, saying: “He’s quite right to say that he won’t debate her on the basis that she’s not a candidate to be prime minister.

“There will be debates with the First Minister in Scotland and the leaders of the other parties in Scotland and that is the right forum for that. It’s about who is going to be prime minister. She is not in the running for that, if she goes and stands in Westminster to be prime minister that will be a different matter.”

Appearing on Radio Scotland, Jack went on: “He’s not running scared at all.”

The remarks came ahead of last night’s Johnson-Corbyn leader’s debate on ITV, something the SNP and LibDems were excluded from. Both raised legal challenges but lost their cases.

A number of other pre-election specials are planned, including a Question Time Leaders’ Special featuring all four of those party leaders this Friday, and a seven-way debate also including the Greens, Plaid Cymru and the Brexit Party the following week.

Both are on the BBC and the broadcaster said those taking part in the final show would be “leaders or senior figures” from each side.

Yesterday the Financial Times reported that Johnson will not appear in that programme because, according to one Tory source, it is “not a top-tier TV event”. The source reportedly told the paper that this is why “big-name performers with stardust” like Sajid Javid and Priti Patel would not be put forward. Instead, Johnson is expected to send relative unknown Rishi Sunak, who is Chief Secretary to the Treasury.

Last night the BBC shrugged off the “not top tier” comment, telling The National: “The BBC has invited seven political parties to send senior representatives to the debate in Cardiff which, along with the other debates and special programming, is a key part of our electoral coverage. We will announce further details of the debate in due course.”

Yesterday Jack also claimed that only an SNP majority in the 2021 Holyrood election will provide the mandate needed for a second independence referendum.

Dismissing the pro-independence stance of the Scottish Greens, who saw their numbers rise in 2016, Jack said: “We’ll see whether or not the Scottish National Party get a majority then – and I mean the Scottish National Party, not in collaboration with other parties, not in any alliances but a Scottish National Party majority, which is what Ruth Davidson pointed out some months ago.”

Responding, Green MSP Ross Greer said: “It’s a shame Alister Jack knows so little about Scotland that he’s unaware Green gains at the last election are what maintained the pro-independence majority.

“What Mr Jack must explain now is why the majority of MSPs elected in 2016 doesn’t count but a majority in 2021 apparently would.”