On Tuesday, 8 March 2016 08:49:08 UTC+1, wrote:
good morning

I have just gutted a four bedroom townhouse over threes floors

I have therefore to decide what heating / hot system I should put back
in as there is nothing right now - not even a copper pipe!!

It is of 1950's construction, so the walls are not very well insulated.

At this point, I would insulate the walls. If you have a cavity, get it
filled. If not, consider whether you want to add external insulation or
internal.

External:
+ The walls act as a heat store, keeping it cool in summer and warm in
winter.
+ No loss of space inside
+ No problem with interstitial condensation (because the thickness of
the wall stays warm.
- May look naff outside, and particularly difficult if you are in a
conservation area.
- Difficulty detailing at roof and windows.

Internal:
+ Wall is outside the insulation, so house heats up quickly when you
come in in the evening.
+ External appearance unaltered
- Need to be careful about interstitial condensation. Need a really
*complete* vapour barrier.
- Some loss of internal space.

When we insulated the inside of our bathroom with 100mm wood fibre
(Pavadentro) it went from the coldest room in the house to the warmest.

- the roof is well insulated.
Really? 200mm of glass fibre?

I am thinking of a radiator system as I am on a limited budget
Sensible enough.

water wise - there are three showers (1 on each floor and it is likely ?
that at least two will require water at the same time.

Sounds like you need a system boiler and a hot water tank or thermal store.

Think about siting the tank and plumbing so that you can fit solar thermal
later, even if you don't fit it now.

I should say that I don't expect to live in the property for more than
5 years at the most so I do not want to pay huge amounts for a renewable
energy system that takes years and years to re-coup the investment.

A nice warm house that you can gloat about how little it costs to heat will
sell much more readily when it comes time to sell. (You may not make the
pound costs back, but the reduction in stress when it sells quickly has
value - and you may make the money back too.)