I take it it turns over okay, just difficult to start?
Yeah. It's an old story. It turns over just fine and even fires quickly but then it idles very slowly (at around 300 rpm) for a couple of seconds before picking up to a more appropriate 1,500rpm. Occasionally it will fail to pick the revs up and just stall out. Very occasionally it will keep turning the engine over for a couple of seconds before spluttering and giving up.
On the second attempt it fires up immediately.
What's weird is that it hardly ever does it in the evening after work. It's almost always in the morning yet I keep the car in my garage overnight. The garage has an insulated electric shutter and the car shares the garage with my gas boiler. So in the depths of winter it will struggle to start in a garage at around 10 degrees but in the evening after sitting outside in drizzle and temperatures near freezing it will start just fine. It has also never done it (I don't think) when I've been visiting friends and family and the car has been parked outside overnight.
The only theory I have so far is condensation forming when I park it up in a garage. I do have a dehumidifier so once the pattern is established this year I might try and find somewhere I can leave that with it blowing into the engine bay to see if it makes a difference.