Fix overheating BMW 318?

I bought a BMW 318 ti compact (1997) about 3 months ago. I used to drive it about 25 miles a day, and 2 or 3 times a week I would drive it to london and back (approx 50 miles each way). The car would do this journey just fine, until one day when i had driven the car for about an hour and a half, smoke came billowing out of the bonnet and i had noticed that the temperature gauge was at its limit (on red) and water was gushing out of the car. I got it towed home and sent it to the garage.

The garage said they had fixed it and so i went back to my old routine, only for it to happen again whilst in traffic in london. (I've now learnt my lesson and constantly watch the temperature gauge!) However, i'm coming to the end of my tether with the car. The other day this nearly happened for a 3rd time after having been in the garage (i didnt let it happen again, because as soon as i noticed the temp gauge reaching red i pulled over to let the car cool down)...

I've had the gaskett changed, a new radiator fitted, its been in the garage 3 times and still its overheating. I dont feel safe driving the car at night on my own and want to know how it can be mended without having to send it to a proper BMW garage as this will cost me a lot more than my local garage, but they obviously cant figure out what is wrong with it!

any advice as to what might be wrong with my car is much appreciated!! can it be fixed at all?!