It is going to be a tight battle for the sixth seat in East Derry, with all eyes on independent unionist Claire Sugden to see if she can hold the seat she took over from the late David McClarty.

Sitting Democratic Unionist Party MP Gregory Campbell increased his vote by a significant 7.6 per cent at last year's Westminster election.The decision not to stand again for the Northern Ireland Assembly, from the last of the North's double-jobbing politicians, comes as a law banning dual mandates takes effectthis summer.

At the 2011 Assembly election, Mr Campbell topped the poll with 18.2 percent of the vote and was joined at Stormont by party colleagues George Robinson and Adrian McQuillan, who narrowly squeezed out the Ulster Unionist Party's David Harding.

Cathal Ó hOisín was elected for Sinn Féin, John Dallat for the SDLP and Mr McClarty won as an independent, after being deselected by the UUP.

The UUP decision not to run Mr McClarty, hugely popular in this home area of Coleraine, was a big mistake. The respected 63-year-old politician, who had been an MLA since 1998 and was a former deputy speaker at Stormont, died in April 2014.

Ms Sugden replaced him and has had a reasonably strong media profile since taking on the role, but has never stood for election before – making this seat, and possibly the DUP’s third, vulnerable on May 5th.

East Derry is a constituency where UUP leader Mike Nesbitt thinks he can make a gain. UUP councillors William McCandless and Aaron Callan are the party's candidates and Mr Nesbitt will be hoping, after a significant period of decline for the party, its new found relevance with voters – two UUP MPs were elected to Westminster last year – will give it a sufficient boost going into May 5th.

In a crowded field – with 17 candidates competing for six seats – the DUP's George Robinson should retain his seat. Even without Mr Campbell, one would expect the DUP vote to remain strong in East Derry. The other DUP incumbent, Adrian McQuillan – or Mr Campbell's replacement on the line up, Maurice Bradley – will also surely get over the line. However, there's no certainty the DUP will hold all three seats.

Mr Bradley, a newspaper production manager, is well established with the voting public, as he has served as a councillor and mayor in Coleraine over the last two decades.

With the SDLP's John Dallat retiring, it is up to Gerry Mullan, its single candidate, to hold the seat for the party.

Here, Sinn Féin could well present a problem for the SDLP. Cathal Ó hOisín is a popular candidate and recently won favour among a broad section of the public in the North for publicly sharing his experience of losing a baby to fatal foetal abnormality during discussions at Stormont about abortion reform.

In 2011, Sinn Feín's Bernadette Archibald received 2,639 votes, but this was not enough to join Mr Ó hOisín at Stormont.

Sinn Féin took one seat, with 21.1 per cent of the vote, and the SDLP took one with 14.9 per cent, so Caoimhe Archibald – Bernadette's daughter, and Mr Ó hOisín's running mate – can garner sufficient support, she is in with a chance of being elected at the SDLP's expense.

Prediction

East Derry is a predominantly unionist constituency. In 2001, the DUP's Mr Campbell defeated the UUP's William Ross, who had represented East Derry at Westminster since 1983. The DUP gained from the UUP at the 2007 Assembly election, and both the DUP and SF made gains in 2003 from the SDLP and an independent unionist.

The SDLP will be working hard to make sure it retains its one seat and Sinn Féin does not take two.

If Ms Sugden has done enough work over the last two years she might be able to see off challenges from unionist rivals. but the UUP expects some of Mr McClarty’s vote to come back to it and is confident of taking a seat.

If there is a shake up and a UUP candidate, perhaps Mr McCandless, is successful, it might be a battle for the final of the six between Ms Sugden and the DUP.

After May 5th it could be:

DUP (3); Sinn Féin (1); SDLP (1); UUP (1).

Candidates
Caoimhe Archibald (Sinn Féin)
Jordan Armstrong (TUV)
Yvonne Boyle (Alliance Party
Maurice Bradley (DUP)
Aaron Callan (UUP)
Stuart Canning (Conservatives)
Tor Christie (Ind)
Amber Hammill (Green Party)
David Harding (Conservatives)
William McCandless (UUP)
Adrian McQuillan (DUP)
Gerry Mullan (SDLP)
Cathal Ó hOisín (Sinn Féin)
Steven Parkhill (Ukip)
George Robinson (DUP)
Claire Sugden (Ind)
Russell Watton (PUP)