I was browsing the net and come across this : -
linky
"1.5 BAR HEAVY DUTY SHOWER PUMP
Boost the power of shower by up to 20 times and run shower after shower! Suitable for use with all Screwfix Direct shower valves.
* Twin Impeller 1.5 Bar Pump
* Continuously Rated Motor
* Produces up to 50' Head of Water
* Vibration Free
* Electronic Flow Control
* BEAB Approved
* 2 Year Manufacturer's Guarantee
Specification: Requires a min. 230mm head of water. Connect to a 13A fused spur."
Its rated for continuous use and 50' of head, im not sure about flowrates thought, but showers should be about the same as water cooling systems.
It is also vibration free, it cost £138 is it any good/worth getting?