The easiest solution (although not the most elegant) will be to cut the mains supply into the cold water tank, cut the cold water outlet pipe (having emptied the tank first of course), and create a bridge between the two with some of that spare hep pipe you have. Thus you can remove the cold water tank entirely and have mains water supplying all the outlets that were supplied by the tank.
Thus you will not require a pump, and since the thermostatic shower will be fed by equal pressures both hot and cold, it will work far better.
Thanx Dextrous that is what ive done, basically linked the tank out i now have mains throughout.