David Simpson was DUP MP for more than a decade but his local DUP association does not have enough members to choose his replacement

Sitting MP David Simpson announced on Wednesday that he would not be standing again.

Mr Simpson, who defeated the then Ulster Unionist leader David Trimble to take the seat in 2005, had been quietly canvassing DUP members for weeks and was keen to stand again for election.

However, last year it was revealed that he had an extra-marital affair with an employee who was also a DUP councillor.

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Mr Simpson – a Free Presbyterian who had spoken out about his Christian faith and the sanctity of marriage – had not addressed the issue publicly and adopted a low profile after the affair was revealed.

On Wednesday, the outgoing MP said: “In recent times it has been well publicised that I made a mistake that brought hurt to my wife and family as well as bringing heartache to another family.

“These were my mistakes and for them I am truly sorry. I have learned from my failings and my wife and children have given me a precious second chance and together we intend to look to the future together.”

The day before Mr Simpson issued his statement, DUP chief executive Timothy Johnston wrote to party members in the constituency to set out how the party would choose its candidate.

Mr Johnston wrote: “We must now move at speed to select a candidate to fight the Upper Bann seat for the party given that Parliament has now dissolved.

“Under our party rules selection of a candidate is conducted by constituency associations who have more than 40 paid up full members on 1st September preceding the selection meeting.

“Unfortunately Upper Bann does not have the required 40 members paid up on that date to enable a meeting to be held.

“Therefore, as set out in our rules, the party officers shall be responsible for the selection of a candidate.”

Despite the association not being allowed to select the candidate, Mr Johnston said that the party officers wanted to hold “an informal meeting” of the Upper Bann association “to hear the views of local members prior to the officers taking a final decision on candidate selection”.

That meeting will take place tonight at Brownlow House and Mr Johnston said that the party was open to applications to be the candidate from “any member of the party” with a deadline of 5pm today for such applications to be made.

Mr Simpson leaves a majority of almost 8,000 votes, meaning that it is one of the DUP’s relatively safe seats.

In the 2017 election, Sinn Féin’s John O’Dowd came in second place, with the UUP’s Doug Beattie more than 14,000 votes behind the victor.

There had been speculation that DUP leader Arlene Foster could put herself forward as a candidate. However, party sources have said that will not happen. The DUP is attempting to use the election as a springboard for the restoration of Stormont and if Mrs Foster was to get elected to Westminster she would have to quit Stormont, a move which would suggest she did not think devolution was returning.

The front-runner is believed to be local MLA Carla Lockhart. Ms Lockhart topped the poll when she was first elected as an MLA in 2016 and then increased her vote to again top the poll in 2017, despite that being a disastrous election campaign for the DUP in which it lost 10 MLAs after the RHI scandal.

Fellow MLA Jonny Buckley, who was first elected to the Assembly in 2017, is also believed to be in the frame. Mr Buckley is highly regarded within the party and was just 25 when elected as an MLA. However, in the absence of any functioning Assembly he has yet to even speak in the chamber.

The other candidate rumoured to be interested is MEP Diane Dodds. She lives in Banbridge in the constituency and will be losing her MEP role in January if Brexit happens then.

One factor in favour of Mrs Lockhart and Mrs Dodds is that the DUP’s sole female MP, Emma Little-Pengelly, is likely to lose her seat in South Belfast and it may not want an all-male group of MPs returned to Westminster.

Mrs Dodds and her husband are two of the DUP party officers.