A by-election will be held this autumn in a strong Labour seat after Rosie Cooper announced she was stepping down as an MP after 17 years.

The Labour MP, who has represented West Lancashire since 2005, said the announcement “will come as a surprise to many people” as she had recently secured reselection to stand in the seat for the next election.

Ms Cooper, 72, said she is stepping down because she has accepted a new role as chair of Mersey Care NHS Foundation Trust.

She held her seat in 2019 with more than 52% of the vote and a majority of 8,336. Labour confirmed to Sky News that a by-election will take place “this autumn”.

Ms Cooper said: “It has been an incredible honour and privilege to have served the people of West Lancashire for the last 17 years. I have loved every minute, even in the most difficult times.

“I appreciate this will come as a surprise to many people, having recently secured reselection to stand as West Lancashire’s Labour Party candidate for the next general election. This was prior to the recruitment process for the Mersey Care position.”

She said she had taken a “considerable period of soul-searching and reflection” before applying for the role, adding: “The events I have faced over the last few years are well documented and undoubtedly have taken their toll.”

Neo-Nazi’s plot to kill for ‘white jihad’

The MP was the victim of a plot to kill her by an alleged member of the banned neo-Nazi group National Action – the same group the man who killed Labour MP Jo Cox was a member of.

In 2018, Jack Renshaw, then 23, of Skelmersdale, Lancashire, admitted to plotting to kill Ms Cooper for “white jihad” and for making threats to kill police officer Victoria Henderson.

On the first day of his trial at the Old Bailey, he admitted planning to kill Ms Cooper with a replica Roman Gladius sword in the summer of 2017. He boasted to other members he had already bought a knife marketed as offering “19 inches of unprecedented piercing and slashing power at a bargain price”.

Renshaw planned to carry out a “politically and racially motivated murder” in support of National Action, the court heard. He denied he was a member of the group.

After killing Ms Cooper, Renshaw told the group he would take people hostage and then demand that PC Henderson came to the scene before he killed her.

Ms Cooper, who was originally a Liberal Democrat, was previously chair of Liverpool Women’s Hospital and a trustee of the Roy Castle Lung Cancer Foundation.

She said returning to the NHS “felt like the right opportunity at the right time”, but means she cannot continue “with my other passion of representing the people of West Lancashire as their MP”.

She thanked her constituents and said she was sad to leave.