Devon and Cornwall's new crime commissioner, Alison Hernandez, will be sworn in today despite being under a police investigation.
The ceremony at Exeter's Guildhall will go ahead even though an outside force is investigating claims she failed properly to declare campaign expenses while she was the Conservative election agent in Torbay. She claims the cost of a battle bus was part of national, not local, spending.
Labour MP Ben Bradshaw says she should step aside while the inquiry continues.
"I just think it's untenable for somebody to run our local police service in Devon and Cornwall who is under investigation, under criminal investigation for such a serious offence and that the public should be expected to have confidence in her performing that role."
"While this investigation is ongoing in the interests of public confidence in this role, Ms Hernandez should not take the oath, she should step aside."
Devon and Cornwall's chief constable Shaun Sawyer said a different force would investigate all allegations made against any constituency or individual.
Eight forces are reported to be investigating the claims surrounding the 2015 general election campaign, but senior Tories have insisted the party did nothing wrong.