Property with no Mains Gas - cheapest options

Whatever choice you make, I would advise against using bottled gas for heating - it will work out cripplingly expensive.

Depending on where you are, bottled gas could cost you anything up to £70 for a 47kg bottle. You can get it cheaper by shopping around, but that seems a pretty commonly quoted sort of top-end price at present.

The denisty of Propane (which is the particular flavour of LPG that the big orange bottles are filled with) is about 0.58kg/l (you will find different figures quoted if you look around - 0.5kg/l is often quoted, but 0.58kg/l is a fairly accurate value), so that means a 47kg bottle contains 81 litres of Propane, give or take.

From the above this gives a price for bottled LPG of anything up to about 84ppl

Now typical average annual usage for heating (for bulk LPG, which is the same animal, only delivered by tanker into large bulk tanks and far cheaper than bottled LPG) has been quoted elsewhere on these forums (http://forums.moneysavingexpert.com/showpost.php?p=40366130&postcount=606) by someone who works in the industry (and therefore should know these things) as 2,500litres, which at 84ppl (worst current case) works out at about £2,100 a year!

You should also note that LPG pricing has been particularly volatile over the past few years, and long-term, it is only likely to rise.

If you are considering LPG heating, bulk LPG should work out significantly cheaper than that (depending on supplier and contract - see the Bulk LPG Cheapest Supplier / Supply Route thread for chapter and verse), but as you're in a mid-terraced house, I suspect that installing and delivering to a bulk storage tank (LPG or oil) is unlikely to be an option.

And remember, if you are considering electric heating, the Feed In Tarriffs for Solar PV generation are currently very favourable although that could change (see http://www.moneysavingexpert.com/news/utilities/2010/10/spending-review-solar-feed-in-tariffs-safe-for-now)