Help! Clutch issues

Hi there,

Was wondering if anyone can offer me some advice on what to do.
My 197 was having some clutch issues recently when it became hot from sitting in traffic and stop start moving, After traffic cleared and I could pick up speed again the clutch would slip revs would go up but nothing would happen with car lacking power loads of revs and then it would catch again would do this in most gears. The bite on the peddle would be very high it would be like it is about to stall before I had movement forward in 1st. Temprature of car would be half way and fan has cut in about 3- 4 times. Once home and cooled down get in it next day and drives fine no slipping.
After getting very fed up with it (and not just happening to me so not my bad driving ) I had new clutch fitted. Problem seem to be solved, until yesterday when went for MOT car had been running in garage for 20-30 minutes and moved about a bit. guy brings car out says my bite on peddle is very high and on way home revs picking up but slipping clutch and no power issue again. Car is hot and stays warm all way home with fan cutting in.
Could this be master cylinder or what else could it be ?? It is driving me mad someone please help me