Andy Street and Ben Houchen go into Thursday’s mayoral elections having run campaigns almost entirely separate from the Conservative party they represent. But this week the respective high-profile Tory mayors for the West Midlands and Tees Valley have associated themselves with one senior Conservative whose endorsement they appear to relish: the former prime minister Boris Johnson. Street has sent out a two-page letter to voters in the West Midlands in which Johnson lavishes him with praise and dismisses the Tories’ record in Westminster. Meanwhile, Lord Houchen’s supporters have promoted a video from the former prime minister appealing for voters in the Tees Valley to re-elect him. Both mayors are facing knife-edge votes. If they lose, Tory rebels are expected to mount another attempt to remove Rishi Sunak as prime minister. Despite the importance of the mayoral results for Sunak, however, it is Johnson to whom both men have turned as the campaign reaches its final stage. In his endorsement of Street, Johnson writes: “Forget about the government. Forget about Westminster. This election is about the next four years in the West Midlands – and who you want in charge. If it were my vote I’d want the person with a record of getting stuff done. And that’s Andy Street.” He adds: “So ask yourself, is kicking the Tories worth four years of a soft-on-crime high-spending bankruptcy-causing Labour mayor? You might not like everything the Conservatives have done. But you won’t like anything Labour would do.” The letter does not feature the Conservative logo, using the flag of the Black Country instead in its header. In his video for Houchen, Johnson does not mention the Conservatives, instead keeping his message focused on the mayor himself. “He is a guy who does what he says he’s going to do,” Johnson says. “Mayor Houchen delivers.” The messages reinforce the central campaign message from both candidates that they are independent from the party they represent and distanced from the unpopular Tory government in Westminster. They also testify to Johnson’s continued popularity among voters the Conservatives normally struggle to reach, many of whom are telling pollsters they intend to vote Labour at the next general election. Street said last month: “I am a proud Conservative but that is totally different to: ‘Do I agree with this Conservative government in everything it’s doing?’” He told the Guardian on Wednesday: “I’ve had a wide range of support including from the prime minister, Boris Johnson, Theresa May and David Cameron. Boris has made it clear in his letter that this is an election about the West Midlands and the choice people have between continuing to support me or ending up with a Labour mayor.” A Labour source said: “Rishi Sunak’s predecessor telling voters to forget about the government is a damning verdict on the prime minister’s leadership. Both Ben Houchen and Andy Street have distanced themselves from Rishi Sunak but seem very happy to put Boris Johnson’s name up in lights. “Rishi Sunak is such a drag that his own candidates clearly feel they need to dump him to win.” One ally of Johnson said the former prime minister had been happy to intervene on behalf of Street, Houchen and Susan Hall, the Conservative mayoral candidate in London whom Johnson praised in a recent Daily Mail column. They would not be drawn on whether this marked a broader return for Johnson to the national campaign trail. A party spokesperson said: “These are local elections, tackling local issues that differ from area to area. The Conservatives have a record to be proud of, and have made huge strides for people in the West Midlands and Tees Valley. “No matter where you are in the country there is a clear choice. Conservatives who deliver more for less or Labour who don’t have a plan.”