The Ministry of Defence is funding £900,000 of paint work to add a Union Flag design to an RAF Voyager, it has been revealed.
The makeover of the currently-grey aircraft, used by the Prime Minister for official travel, consists of a red, white and blue transformation taking place in Cambridgeshire.
Downing Street said the "national branding" represents "value for money" amid criticism from some MPs.
Minister for Defence Procurement, Jeremy Quin, said: "The project will be carried out by Marshall Aerospace Defence Group (MADG) in Cambridge.
"The decision to repaint the VIP Voyager - and approval of a design that best projected Global Britain - was taken on a cross-Government basis, to be funded by the Ministry of Defence."
The makeover, which is believed to have started earlier this month, will allow the Voyager to retain its air-to-air refuelling capability and continue its "vital military role", according to a spokesperson for the Prime Minister.
"It will have national branding and that will mean that it will be in line with many other leaders' planes," they added.
The Lib Dems' defence spokesperson, Jamie Stone MP, recently described the work as an "absurd waste".
Labour MP Emma Hardy, meanwhile, said: “For goodness sake. Please can we have a grown up as a Prime Minister instead of a child."
In 2018, then as foreign secretary, Mr Johnson said he would like to have a "Brexit jet".
He made the comments after questioning the availability of the RAF Voyager, which is also used by members of the Royal Family and other senior politicians.
Mr Johnson was also quoted as asking: "Why does it have to be grey?".
The Voyager began transporting VIPs, including other Government ministers, in 2016 following a £10 million refit.
It was announced at the time that the 58-seater transport aircraft would continue to conduct air-to-air refuelling missions for the RAF when not in use and that it had retained its military livery.
Cover image: The RAF Voyager being transformed from its current grey colour (Picture: PA).