Crank but struggles to start
 

Morning all, new here.

I have a 2007 cooper S 1.6 petrol which is cranking but takes a couple of attempts to start and is then a bit juddery until it has warmed up. I have changed the Cam sensor which was the only fault code it was throwing up but this still hasn’t sorted the issue. Does anyone have any ideas. I’m edging towards the high pressure fuel pump but thought I would see if anyone had any other ideas first. Thanks