E53 startup problems

[Lozzz]

Hi I'm new to this forum, but have used information off here many times and. Come across some sound advice.

Basically I have an e53 x5, a couple of months ago I went to start it as usual but it took slightly longer to fire up, it was a hot day and it was the first time I started it that day, didn't think much of it until a few weeks later when it did it again,
the starter carries on spinning until I give it a rev to get it going. It has got more and more frequent, mostly the first time I start it in the day when the engine is cold but sometimes if I leave it a few hours.
Now it can take 5 plus seconds of cranking to get it started even pressing the gas doesn't do much. It is only intermittent and I can put my finger on why and when it will do it e.g ambient temperature etc apart from when the car has been sat for a few hours.
I've tried sitting in for a few seconds with the ignition on to let the fuel pump prime but it's still the same, so no leaky injectors.

Any help appreciated