We know of two already and 2017 hasn’t even started
One of the big trends in recent times, as the chart shows, has been for a big increase in by-elections caused by other than the death or health of the sitting MP. This year there’ve been seven contests with five of them in the “other” category. Ogmore and Toting were caused by the sitting MP either switching to the Welsh Assembly or becoming Mayor of London. Two of the other three were linked to BREXIT while the final one related to the government’s decision on Heathrow.
Looking to 2017 there are signs that we could have another big year. The creation of the big combined authority elected mayors provides opportunities for other sitting MPs as well as twice-failed LAB leader contender, Andy Burnham.
Also we have the trials and tribulations within Labour following the Corbyn re-election with reports that other MPs are ready to step down and create by-elections like the upcoming one in Copeland.
We still don’t know what the Electoral Commission is going to do following the Michael Crick Channel 4 Tory GE2015 expenses investigation. Whether that leads to by-elections is hard to say but certainly there’s an expectation within UKIP that Nigel Farage might be able to have another stab at Thanet South. LAB and the LDs have similar hopes.
A betting market on the total number in 2017 might be a good idea. I’d go for 7+.