Labour activists campaigning before a byelection in a safe Conservative seat have been told to leave if they feel unable to be respectful to Tory voters, as the party attempts to tackle the assumption that it cannot compete in true blue heartlands. Direct Tory attacks are also being scrapped or significantly toned down as Labour strategists try to convince voters in the Mid Bedfordshire seat that their candidate will put the “constituency ahead of the party” if necessary, should he win the seat. The change in approach comes with Labour desperate to make an impression in the constituency, as part of its strategy to prove it can win over some voters who backed the Conservatives in 2019 and over a longer period. A huge Labour operation is already under way in the seat, despite the fact that the byelection has not yet been officially called. Labour immediately targeted the seat to test its appeal to soft Tory voters when Nadine Dorries, the former culture secretary, said she was standing down last month. Dorries, a close ally of Boris Johnson, said she would quit with immediate effect after being prevented from having a peerage on Johnson’s resignation honours list. However, she has yet to formally resign. Figures in both Labour and the Tories believe she will do so at a time to cause maximum damage to Rishi Sunak, who she blames for both preventing her elevation to the second chamber and precipitating the end of the Johnson prime ministership. Some expect her to formally resign the day after the three byelections that are being held on 20 July. With Dorries recording a majority of more than 24,600 votes at the last election, Labour planners know the seat is a long shot – with the Liberal Democrats also said to be making a serious attempt for the seat. However, as part of the Conservative-wooing exercise, Labour activists have been put on notice about their attitude to those who say they are lifelong Tories. “It’s about listening to what the voters here are telling us,” said a senior Labour source. “A group of activists that came here were told: ‘If you can’t have a respectful conversation with a Tory voter, you have to go home.’ We’re finding that a lot of people say they are Tory voters, but when you ask them, they say they can’t vote for them. “We have ended all direct Tory attacks. We just don’t need to do it. We have simple messages like ‘on your side’. There are no direct attacks on Nadine. We simply push our candidate as someone who will put the constituency ahead of the party and hold regular meetings in the seat.” Tory whips remain uncertain over Dorries’s plans. She is already preparing to cause problems for Sunak by publishing a book about the fall of Johnson’s administration just days before the Conservative conference. It is being billed by her publisher as a tale of “treachery and deceit at the heart of the Westminster machine”. Last week cabinet secretary Simon Case revealed he had reported Dorries to the Commons speaker over a “forceful” message she allegedly sent him stating that she should be added to Liz Truss’s resignation honours list. Dorries has previously been criticised as not spending enough time in the Mid Bedfordshire constituency – something she has disputed. She has already endorsed the Tory byelection candidate, Bedfordshire’s police and crime commissioner Festus Akinbusoye. The Labour candidate, Alistair Strathern, is a Bank of England official. In his literature, he does not name Dorries, but says he would be “the hardest working, most accessible and visible MP you’ve ever had” and would “put Mid Bedfordshire first and party second”. Party officials believe he has the ability to appeal to disillusioned Tory voters. “It’s like he was made in a lab for it,” said one. “He looks half farmer, half banker.” The determination to make a serious attempt on what is one of the safest Tory seats comes after officials were frustrated by the assumption that the Lib Dems were the most likely challengers. “We want to show in this campaign that Labour can win votes in rural parts of the country, that Labour can win votes directly off the Tories,” said a senior party official. “We were in second place in Mid Beds at the last election. “Given the central part of our general election plan is to take votes directly off the Tories, we want to show in these byelections we can do that.”