depends greatly on whether you opt for a good quality boiler or a crap one i.e. you can pay 450 for a heatline condensing combi or 1200 for a top of the range worcester bosch greenstar or a vaillant.
if you then opt for basic (rather than designer) radiators, thermostatic valves your looking at around 2500 - 3000 (birmingham prices)
throw in a wireless programmer/room stat then another 100 on top of that.
make sure you discuss with your installer what boiler he is going to fit as some will fit any old crap because they are getting incentives from their suppliers. get in writng what boiler he is going to fit or specify one yourself. you also need to discuss the power of the boiler he's going to fit. the heatings not a problem but for a fast supply of hot water you need a more powerful boiler. fit an underpowered one and your not going to be happy.
i would reccomend a vaillant ecotec plus 31kw which is their mid range boiler and their best selling model, i think there around the 900 mark.