Found that the hot water cylinder was leaking earlier this week and am
planning to replace tomorrow. I need an indirect combination hot/cold
one with ideally a 150/40 litre split. I was going to order off BES for
£196 but although they offer Saturday delivery they don't guarantee it
will arrive (my fault for not ordering earlier in the week!)

If your mains is good flow and pressure, I wouldn't fit a gravity fed
system. It may be cheaper, but it is incapable of running a shower without a
noisy pump. It also solves the loft mounting problem, as there is no heavy
cold cistern required.

Christian.