The two paintings, one costing £70,200 by Belfast artist Cathy Wilkes and the other at £18,775 by photographer and installation artist Willie Doherty, were paid for by the Government Art Collection fund.
The fund is most paid for through contributions from donors but is supplemented by taxpayer cash.
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The artwork was purchased at a time when the government chose to freeze pay rises for key workers, including nurses and police officers.
Following the Daily Mirror sharing the costs of the artwork, Labour MP Neil Coyle tweeted: “As his Government cuts Universal Credit and freezes frontline nurse/police pay, Johnson has found more money to treat himself. Again.
“He could not be more out of touch.”
Labour MP for South Shields Emma Lewell-Buck told the Mirror: “The selfishness of this Prime Minister is galling.
“When shelves are bare in my local food banks, businesses have gone to the wall, public sector and key workers have suffered pay freezes and cuts, his priority is once again himself.”
Downing Street has hit back, defending the spending as necessary to “promote the creativity of British art and culture.”
A Government spokeswoman defended the spending, saying: “The Government Art Collection helps to promote the creativity of British art and culture by showcasing its works in the UK and across the globe.
“It acquires new works after consulting and securing the approval of an independent expert panel, and the majority of funding for acquisitions comes from philanthropic sources – not taxpayers’ money.
“The Government Art Collection is committed to public engagement and lends extensively to public exhibitions and collaborates with public facing national events and through its digital platforms.
Former culture secretary Ed Vaizey, now a Tory peer, also supported the purchases, saying: “Govt art collection has supported British artists for 120 years – a unique cultural asset for our country.”
He added: “(Boris Johnson) would have had no involvement in acquisition, which wld have come from existing budget.”