Image caption Patrick Doherty became the victim of voter fraud during the UK general election

Will the real Patrick Doherty step forward?

That's the question election workers were left asking in Foyle last week.

We know of at least three Patrick Dohertys - but only one got to vote.

The other two were turned away because their vote was taken by a man who shared their name.

Could it be the same Patrick Doherty who voted early and often on polling day? That's the suspicion.

'Very convincing'

And are there other Patrick Dohertys out there who stayed at home but whose vote ended up in a ballot box?

Welcome to the murky world of electoral fraud.

"The Patrick Doherty who appeared in front of us was very convincing, he called out his name and address and flashed his ID," one election worker said.

Image caption Only 169 votes separated the winner from the lose in the Foyle Westminster constituency

"As we looked for his details he even told us his middle name.

"It wasn't until another Patrick Doherty walked through the door an hour later with his polling card and ID that the penny dropped and we realised we had been conned."

So how easy is it to pull something like that off?

"All they have to do is scan the electoral register, note all the Patrick Dohertys, remember their addresses and then go around their nearest polling station," he said.

"But they have to make sure that the real Patrick Doherty doesn't show up at the same time.

"It's easier if they use the register of non voters, then they know for sure the Patrick Dohertys who are unlikely to show up."

It's an old trick which is now back in the spotlight as some parties here are turning up the heat on electoral fraud.

It comes as no surprise that places like Foyle are getting most attention where only 169 votes separated the winner and loser.

The SDLP's Mark Durkan lost the seat to Sinn Féin's Elisha McCallion.

Knock on the door

The police have now been asked investigate a "small" number of reports of electoral fraud passed on to the chief electoral officer.

History tells us the thief who stole Patrick Doherty's vote is unlikely to get a knock on the door.

But the extra attention around electoral fraud is about putting a marker down for the next election.

While that may lead to more scrutiny next time around, it's unlikely to stamp out a problem which has been around for as long as votes have been cast.

Tackling the problem at government level can also come at a cost.

In 2002 the Electoral Fraud Act was passed at Westminster. It tightened controls around voter identification and absent voting in Northern Ireland, but it also resulted in 120,000 voters being wiped from the register.

There is a balance to be struck between making it easier for voters to mark their ballot papers and making it harder for the mystery Patrick Doherty to mark more than just his ballot papers.