Hi guys, thanks for your reply. Apparently, there is a Warwick/Warwix
(I've seen both spellings) flange to let me fit above the tank, simply
by replacing the vent pipe from the top of the tank. To me, this is
preferable for 2 reasons: first, I don't like the idea of cutting into
the tank; second, I haven't really got the space to fit it anywhere
else.

The challenge I have over the piping is this: I have 2 feeds on the
pump, 1 in 1 out. I run the inlet pipe to the in side of the pump and
I run the outlet to the original feed entry of the tank (I'm looking to
boost pressure throughout the house, primarily to a large washing
machine). Where does the vent line go? Sorry if I'm appearing dense,
but this has definitely got me confused.

I need the prv because I already have a power shower fitted and the
extra pressure will blow the seals in it.

Incidently, the pump will probably be 2 bar, as I am intending to build
an en-suite and use the pump to feed the shower in there.

Thanks
Alan