1.4l Petrol 206 2004 - Very strange fault

For a couple of months ago I was driving on the motorway and the car began to occasionally lose power, whilst I was keep the accelerator in the same position.

The next day I went to drive to work and the car was losing power entirely, even with full throttle. Additionally lots of white smoke/steam was coming out the exhaust. I called out the RAC, who replaced the coil pack and spark plugs. However this did not solve the problem.

Since then the car has been occasionally stalling when coming to a stop (basically when i have been pushing the brake and the clutch at the same time whilst slowing down - however this has been very intermitted, once every few days).

Today I was driving and it was losing power again, and again white smoke/steam was coming out of the exhaust.

The only thing I can think of is if it something to do with the cold and damp weather, which it was on the previous time also. I do not have a great knowledge of cars, but even my friends who know a bit more than me are at a loss.

It passed its MOT fine last month. The garage are aware of the issue, but do not know what is causing it. They are happy to do exploratory work, but at a cost... I am tempted to buy a new car but would really like to keep my current one.

Any ideas...?

Dan