I'll definitely get some decent loft insulation up there, seems to be pretty cheap. I'm trying to find out why my first gas bill was £65/month, and the second was £175/month, despite temperatures not being all that lower; but certainly I'll do everything I can re insulation.
I paid £1 per roll from an offer nPower (delivered by local builders merchant) had for any (non npower) consumer. Looking at their site, it looks to have increased to £3 per roll but still cheap!
Without seeing your heat loss calc (earlier link) it is hard to say for certain, however, £175 to me for a 3-bed detached indicates you have a fault somewhere (gas leak, room stat, boiler or hot water leak?)
Have you noticed the boiler coming on when there is no demand for heating?
Re. keeping the house at a constant temp rather than letting it cool down all the time; what temp what you suggest is the lowest to keep it at (for rooms that aren't used much), and would you do this for all individual rooms, even bathroom etc. that is only used for maybe 1 hour a day max.? Going to get some of those individual timer valves for a number of rooms.
I have programable room stat which allows me to set different temp's at different times of the day. There is always someone at home so depending on the time of day, and day of week, my house will be between 19-20C until midnight.
2. Thanks, I'll remove them again. The lounge seems to get hotter much quicker than other rooms downstairs (with the rads on the same setting, and doors either open or half-open): is there a way to decrease the heat output of the lounge radiators (not just the TRVs) so it's more even?
Yes, you need to make sure the radiators are balanced (search on here or Google for loads of info on how to do it! (You basically alter the lockshield valves on all rads to make sure they are heating up equally and ideally with a 20C drop (or as high as possible upto 20C) between the flow and return pipes)