Daf 45 150 won't idle or rev up on start?

Hi, has anyone got any ideas where I need to start looking

I have an ex Army Daf 45 150 - 1996 which has always started and run like a dream.

I decided to run it up after 3 weeks after this cold spell and this is what happens.

turns over fine, then starts but the revs do not pick up when the throttle is pushed down....they stay the same. When it first starts up I get a lot of white smoke from the exhaust and then it goes normal colour. If I take my foot off the throttle it will cut out.

I'd be grateful for any help where to start looking first.