Updating my problem with restarting a M54 motor after it had been sitting for a month and the dealer couldn't find a fault and put it down to "sticking piston rings" I found this on another forum for E46's which gives the answer, so it did have nothing to do with the vanos unit. Hope this helps someone in the future

"BMW e46 sits for 2 or more weeks and won't start with no fault codes. This is a well known problem to them. Why ? With age & miles: something or things are not operating in spec anymore so the engine doesn't start the first time, the start up sequence dumps a bunch of fuel into the cylinders each time you crank, which washes the oil off the compression rings so you then have very low compression - not enough to start the engine.

How to fix it - if the engine doesn't start the first time, put the accelerator to the floor and crank the engine, it will generally start. In my case I had to take the plugs out, put a 1/2 teaspoon of oil (one squirt from an oil can) into each cylinder (get a long skinny hose ...) turn over the engine a few times, put the plugs in, and the engine starts immediately, once the smoke clears, it runs fine"