Shower no pressure

[stebed]

I have recently fitted a crossfire shower valve (from the bathstore) The previous shower was fine but the bathroom needed updating. My question is the new shower has no real power. It is run of the hot tank and the cold tank in the loft. First question, what pressurises the hot water tank? The cold tank relies on it's head for pressure (which is about 1 metre). The cold water feed into the house is very high but due to the system I guess this has little effect on the shower output?

Is my assumption correct? And in your experience would a shower pump solve the problem?

Thanks in advance.