Five Conservative members of parliament are under investigation over attempts to lobby judges ahead of a hearing in relation to the disgraced former Conservative MP, Charlie Elphicke. Parliament’s sleaze watchdog confirmed it was investigating the MPs; Roger Gale, Adam Holloway, Bob Stewart, Theresa Villiers and Elphicke’s estranged wife, Natalie, who succeeded him in his Dover and Deal seat. Using Commons stationery, the group wrote to senior judges to intervene in a hearing on whether references to support the former MP at his sentencing for sexual assault could be made public. They are being investigated by Kathryn Stone, the parliamentary commissioner for standards, for “use of facilities [stationery] provided from the public purse” and for “actions causing significant damage to the reputation of the house as a whole, or of its members generally.” A Conservative peer and former minister who had also put his name to correspondence sent by the MPs was found earlier this year to have breached parliament’s code of conduct. Lord Freud apologised and agreed to make a personal statement to the House of Lords after investigations were launched when a member of public complained after reading a Guardian report that the head of the judiciary had admonished Freud and five MPs over their attempted interference. It had not been Freud’s idea to contact the judges and he had not realised that the letters were being sent on House of Commons headed paper, according to the report into his conduct. Freud, Gale, Holloway, Stewart and Villiers were among those who provided character references to support Elphicke at his sentencing in September, when he was jailed for two years after he was found guilty of of sexual assault against two women. The Guardian then lodged a request to access the references provided by the parliamentarians – who were not known at the time – and a date was set for a court hearing. Freud and the MPs subsequently identified themselves as the authors. However, they and Natalie Elphicke then wrote to senior judges, copying in the judge who was due to oversee the hearing, expressing concern that “matters of principle” should first be considered by senior members of the judiciary and by parliament. In the same list published on Monday, the parliamentary commissioner for standards confirmed that Boris Johnson was being investigated for a possible breach over a luxury £15,000 Christmas holiday in the Caribbean. Also under investigation are Claudia Webbe, the MP for Leicester East, who was suspended from the Labour party last year, and two Tory MPs, Jonathan Gullis and Owen Paterson.