thanks for all the replies to my asking for advise on the above.
I have installed a pump I bought from ebay, it came from germany 800W 4bar. I fitted a Clarke EPC1000 control unit from machine mart. I bought 2 full bore lever valves so as to either stop the water from being sucked from the tank or from being sent to the water outlets.
I have used 25mm MDPE pipe and fittings but instead of using a header tank, I decided to run the pipe under my decking and into the kitchen under the cupboards. it exited through a wall into the bathroom. As the pipe was going through the kitchen I also installed a tap for the washing machine.
I also fitted a water filter at the pump so as to allow the filtration of any debris that made it to the pump.
All it is left to see is how much I can save over the next 12 months.
Thanks again Dave