In a bid to rally party members, Ms Rayner ran through the policy pledges made in recent days and insisted Labour would be “radical, responsible, realistic” in power.
By contrast, she described Liz Truss’s new Government as a “ministry of all the talentless”, adding: “When I looked at the benches opposite last week, I thought the clowns had escaped the circus.”
On Mr Johnson, ousted from Number 10 after a series of scandals which included lockdown-busting events in Downing Street, Labour MP Ms Rayner said: “I do owe him one apology.
“I said he couldn’t organise a booze-up in a brewery. Turns out he could organise a booze-up pretty much anywhere, just a shame he couldn’t organise anything else.
“We’re a party with a serious plan, he had a plan for a serious party.
“I’ll miss one thing though. As inflation ran out of control, at least his jokes were one thing that got cheaper every week.
“But the real problem wasn’t that his jokes were so cheap, it was that his mistakes were so expensive.
“He ended his time claiming he was forced from office by the ‘deep state’. The only deep state that forced him from office was the one he left our country in.
“Sorry conference, I had to use all my Boris lines now while he’s still remembered and while everyone knows who he is before he becomes a footnote of failure in the history books.
“At least that’s what the new Prime Minister must be hoping for because he’ll be sat on the backbenches plotting his comeback, with a glint in his eye, thinking: ‘I wasn’t so bad after all was I?’
“What a sorry state of affairs.”
Ms Rayner earlier mocked Ms Truss for having “crashed the pork market”, a nod to the Prime Minister’s enthusiasm for the sector when environment secretary.
She said of the Conservatives: “Tough on crime? They brought crime to Number 10.
“Defenders of the free market? The market’s in free-fall. England’s green and pleasant land? Frack it.
“From the party of stability to causing earthquakes. From the party of business to a slap down from the IMF. From the party of serious government to the party of parties.
“Liz Truss has even crashed the pork market. Now that is a disgrace. You’d think that snouts in the trough was the one thing they could manage.”
Labour’s conference concluded with renditions of The Red Flag and Jerusalem, with Ms Rayner and Labour leader Sir Keir Starmer joining in.