The Labour leader was spotted at the department store's Trafford Centre outlet while on a visit to Manchester on Thursday, in what appears to be a light-hearted jibe at the prime minister.
Mr Johnson’s luxurious update of the Downing Street residence was reportedly inspired by a desire to get rid of what a visitor described as the "John Lewis furniture nightmare" left behind by his predecessor, Theresa May.
Some reports claim Mr Johnson and his fiancee, Carrie Symonds, splashed out on £840-a-roll wallpaper in a revamp inspired by top designer Lulu Lyttle.
The prime minister, however, is unlikely to see the funny side of the Labour leader’s joke, after the Electoral Commission announced earlier this week that it is to investigate how he paid for the expensive redecoration of No 11 Downing Street, which some reports suggest cost up to £200,000.
Mr Johnson has said he personally covered the cost of the work, although he and his office have repeatedly dodged questions on whether the invoices were initially paid by a wealthy Tory donor or Conservative Party HQ.
Earlier on Thursday, Mr Johnson, 56, insisted he is a fan of John Lewis, seen by millions of people across the UK as an aspirational place to shop.
When asked about reports relating to the refurb during a visit to King Solomon Academy in west London, Mr Johnson told broadcasters: "The one thing I object to in this whole farrago of nonsense is I love John Lewis.
"But what I will say is what people want this government to do is focus on their priorities."
Ms Symonds, 33, reportedly saw the lavish overhaul as necessary to rid the prime minister's residence of the "John Lewis nightmare" left behind by his predecessor Theresa May, according to Tatler magazine.
The taxpayer funds a £30,000 annual allowance for refurbishments, but the redecoration, which reportedly involves the company Soane has stretched beyond that.
Some reports suggest the upgrades hit the £200,000 mark while a leaked email suggested Tory peer Lord Brownlow was making a £58,000 donation to the Conservatives "to cover the payments the party has already made on behalf of the soon-to-be-formed 'Downing Street Trust"'.
Mr Johnson said he did not believe "there is anything to see here" when asked about the Electoral Commission's investigation, telling reporters: "What we are doing is focusing on the stuff that really matters."
On Wednesday, John Lewis made a light-hearted foray into the row, joking in a tweet that it has home decor to suit the tastes of “*almost*” everyone.
Additional reporting Press Association
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