If you upgrade the electric shower you may need to upgrade the existing cable and protection circuit, this is a job for an electrician and not a plumber, electric showers are mains water supplied so the pressure should not be a problem. Have you tried replacing your shower head with a free flowing item which would help your lack of pressure, the existing head may well be clogged up.
Oooh, well I'm in a ground floor flat, in an old fashioned tenement with two flats above me. The current shower is electric (I flick a switch to turn it on before having a shower) and is annoyingly weak. The pressure in the taps is pretty good, and the heating and hot water comes from a combi boiler. Thanks for your advice!
Speak to a plumber, what you can have depends on yorur boiler and heating system and if you have a pressurised system or gravity fed with tanks in the loft (more likely if your water flow isnt good). I wouldnt recommend electrical showerss as the flow rate is often a bit weak, esp in winter.
What is your pressure like? What sort of heating do you have? Those will have the biggest influence on what shower you can/should have? My plumber also does the electrical work (but I don't know if that is normal). I imagine you would get a plumber to do the job and he would contract out the electrical work if he felt he couldn't do it but still be responsible for it, iyswim.
Your best bet would be to speak to a plumber about what you can/can't have and then start looking at different models within that range.
I'm planning to "revamp" the bathroom. Can't afford to totally replace it and the plain white bathroom suite is actually OK, so I will be removing and replacing the previous occupant's horrid terracotta tiles and putting in a new shower, shower screen, mirrors etc. It has to be a shower over the bath because of lack of space. The current shower works but is a bit of a pathetic dribble - I want something powerful! I was looking at showers in B&Q. They ranged in price from £100 to about £250. Some were called electric showers, others power showers. Which do I want? What about brands? Will I need to install some kind of pump to get the pressure up? Is this a job for an elecrtician or a plumber? Help!