Tonight's Oldham West and Royton by election will be a fascinating crash test.
We're about to find out what happens when the Ukip's accelerating northern force collides with Jeremy Corbyn's huge Labour mandate.
And it doesn't look pretty for Mr Corbyn. He's only been up here once in this campaign and traditional Labour voters aren't happy with his unilateral disarmament, doubts about shooting terrorists or failing to sing the national anthem.
Ukip, on the other hand, are so happy with Mr Corbyn's performance they've put him on their election leaflets. Oh dear.
Two things may save this for Labour:
- A very strong local candidate - Jim McMahon
- A large Pakistani and Bangladeshi community (around 20%) who won't desert Labour for UKIP.
But tonight Nigel Farage told me that if Ukip came within 3,000 votes of Labour in Oldham, then next time they challenge Labour in the North, they will win.
The full list of candidates:
- Conservative: James Daly
- Green: Simeon Hart
- Labour: Jim McMahon
- Liberal Democrat: Jane Brophy
- Monster Raving Loony: Sir Oink A-Lot
- UKIP: John Bickley