Former prime minister Gordon Brown has said the Conservative government will not be remembered for its convictions, but the convictions of Boris Johnson and Rishi Sunak.

Speaking at a rally in Edinburgh as he and four prominent Labour politicians launched a group aimed at reforming the UK, the former premier took aim at the Tories as he talked up his party’s chances at the general election expected next year.

The push comes six months after a report released by Mr Brown – commissioned by Labour leader Sir Keir Starmer – which suggested the abolition of the House of Lords and its replacement with an elected senate and the furthering of devolution to the nations and regions of the UK.

The reason for reform, the former premier said, was brought on by the party that has occupied Downing Street since 2010.

He added: “Now, why do we need change? Well, since I was around in politics, we’ve had five Conservative prime ministers, we’ve had six chancellors of the Exchequer, we’ve had 10 business secretaries, we’ve had 11 justice ministers.

“And of course, that’s all contributed to 13 years of austerity.

“This Government will not be remembered for its conviction, it will be remembered for the convictions of Boris Johnson, Rishi Sunak, 100 fines, sentences and of course a whole series of questions still to be answered about how the Government acted during this period.”

In a speech where he also dubbed Scottish Labour leader Anas Sarwar as the likely next first minister after the 2026 election, Mr Brown poked fun at the turmoil engulfing the SNP in recent months.

Referencing the arrest of former chief executive – and Nicola Sturgeon’s husband – Peter Murrell and then treasurer Colin Beattie, Mr Brown said: “You may not remember the slogan ‘free in 2023’.

“Can you imagine the posters now around the country? The face of Nicola Sturgeon ‘free in ’23’, the face of Peter Murrell her husband ‘free in ’23’, the face of the treasurer ‘free in ’23’?

“I think the best they can hope for is keeping out of prison.”

He also weighed in on a recent spat between the SNP and the pro-independence campaign group All Under One Banner.

The group hit out at the party hierarchy after it planned its special conference in Dundee for the same day.

He said: “The problem with All Under One Banner – the leader of the SNP has refused to speak under this banner, the leader of the other independence party the Greens has refused to speak under this one banner.”

Mr Brown also mistakenly said the march was due to take place in Glasgow on June 25, when it is actually to be held in Stirling on the day before.

Meanwhile, Anas Sarwar made a commitment to the more than 300 people in the room that Scottish Labour would lead the party to a majority at Westminster in the next election.

“I’m going to make you a promise and a commitment today,” he said.

“There used to be a time when people thought that Scotland would hinder, or stop or make us not achieve a UK-wide Labour government.

“I can promise you this – come the next general election, Scotland’s going to lead the way to deliver that majority Labour government.”