What could be the cause of white smoke from the exhausts. It has a smell of fuel/gases coming out. Sometimes when engine is ruining but stationary it is happening and when accelerating quickly. Would this also cause a bigger fuel consumption? 
It’s a 59plate so is an oldish car. But drives perfectly . Struggling to figure out the cause of it. Has had some work done in the hope of fixing it but no look so far. 

Hi Stephanie,

Welcome to the forum.

What engine is in your car, diesel or petrol, also what size 1.5/2.0 etc.

Due to emission standards back boxes tend to be horrendously large these days, this coupled with a warm engine and cooler air temp can create condensation. On start up this may be the cause of the white smoke.

You will usually see this reduce when the engine reaches temp, though on colder mornings/days you'll still see white smoke.

Does yours lessen as the car gets used or stay the same?

You mention MPG, are you seeing a reduction?