Boris Johnson loyalist Ms Dorries, who resigned from the House of Commons in 2023, said she made the decision to join Reform because the Conservative Party was now "dead".
Despite Education Secretary Bridget Phillipson winning 175 nominations from Labour MPs to Lucy Powell's 117, bookmakers StarSports this weekend made Ms Powell 4/6 favourite with Ms Phillipson at 5/4.
Sir Keir Starmer previously turned down a US request to use British bases for its campaign against Iran. But on Sunday, the PM said the nature of the request, and therefore the answer, had changed.