The senior Labour MP Conor McGinn has had the whip suspended after a complaint was lodged against him under the party’s independent complaints process, the Guardian has been told. The MP for St Helens North, who played a key role in getting Labour ready for the next general election until September, is now under investigation. McGinn, 38, who has also had his party membership suspended until the case is resolved, said he was confident the complaint – the nature of which is unknown – was “entirely unfounded”. In recent weeks the MP, who is regarded as an ally of the Labour leader, Keir Starmer, returned to work at Westminster after time off dealing with a genetic heart condition. In a statement, McGinn said: “The Labour party has informed me that it is automatically required to apply a temporary procedural suspension while a complaint is investigated. I have not been told the details of the complaint but I am confident that it is entirely unfounded. I strongly reject any suggestion of wrongdoing and I look forward to the matter being resolved quickly.” In his role as deputy national campaigns coordinator, working with the Labour MP Shabana Mahmood, McGinn was part of the team credited with strong local election results in May, when Labour won back votes in the “red wall”, as well as the Wakefield byelection in June. Previously, he supported the successful campaign for Helen’s law – to get the government to introduce tougher penalties for murderers who refuse to reveal the location of their victims’ remains. He also moved the Commons amendment to extend the equal marriage law to Northern Ireland. McGinn, who entered parliament in 2015, becomes the fifth Labour MP to face investigation under the party’s new complaints process, which was brought in earlier this year after it was censured by the equalities watchdog over its handling of antisemitism. The MP Neil Coyle had the whip suspended after allegations he made racist comments to a journalist in a House of Commons bar in February. Nick Brown, who had been chief whip for every Labour leader from Tony Blair onwards, was stripped of the whip in September after an unspecified complaint. The Ealing MP, Rupa Huq, had the party whip suspended for making what were described as “racist” comments about the former chancellor Kwasi Kwarteng at Labour conference in September, for which she later apologised. Christina Rees, who was shadow Wales secretary under Jeremy Corbyn, lost the whip in October after allegations of bullying her constituency staff. All four are still under investigation and sitting in the Commons as independents. Sources said Labour’s chief whip, Alan Campbell, informed the party’s parliamentary committee, which represents MPs in their dealings with the leadership, of McGinn’s suspension. Under party rules, once an MP has been administratively suspended and is under investigation, they have the party whip temporarily suspended as an automatic precaution. The complaints process, signed off at the party conference last autumn, covers all protected characteristics, including race, disability and sexuality, and all forms of discrimination.