Britain's opposition Labour Party on Tuesday called for an investigation into whether Prime Minister Boris Johnson's press secretary "knowingly misled" the public over the refurbishment of his official Downing Street flat. Dominic Cummings, who was Mr Johnson's key adviser on the Brexit campaign and helped him to win an election in 2019 before a bust-up last year, said on Friday that the prime minister wanted donors to secretly pay for the renovation. Mr Cummings said he told Mr Johnson that such plans were "unethical, foolish, possibly illegal". Labour's deputy leader, Angela Rayner, wrote to Simon Case, the head of the civil service, asking him to investigate Mr Johnson's press secretary's answers about the affair this year. Allegra Stratton, a former BBC journalist, was his press secretary from October until last week. According to Labour, Ms Stratton last month told a briefing that "Conservative Party funds are not being used to pay for any refurbishment of the Downing Street estate". But it has since been reported by British media that the refurbishments were funded through a loan from the Conservative Party. "As a special adviser, Allegra Stratton is bound by the Civil Service Code, which sets out standards of integrity and honesty required from public officials," Ms Rayner said in a letter to Mr Case. "I would urge you to build into your review an investigation into whether the former press secretary knowingly misled journalists and the public, or was misled herself by senior members of the government who seem intent on a cover-up." Downing Street said money from the Conservative Party was not being used to pay for the refurbishments, without saying if it had been in the past. "Any costs of wider refurbishment this year beyond those provided for by the annual allowance have been met by the prime minister personally," it said. "Conservative Party funds are not being used for this."