I totally agree with Richie in that a gas hob with a fan assisted electric oven is probably the best combination. Gas hobs are far more controllable than electric ones in that the moment you turn them down, they react. Electric hobs respond more slowly and will never see a professional Chef trying to cook on an electric hob.
A fan assisted electric oven (with an automatic facility) is very convenient and you have no worries about the gas not igniting when the automatic facility is being used.
I wouldn't risk going all electric. Future predictions about energy supply suggest that longer term the UK could be increasingly vulnerable to power cuts, and at least with a gas hob you can still boil water in a sausepan to make tea, and produce a variety of meals in saucepans & frying pans.
As to which method is cheaper I'm not sure. The secret is to remember to turn the control knob down to Low whatever type of power is used, rather than let everything boil away on high volume which doesn't cook it any quicker.
I currently have a built-in electric grill. I absolutely HATE it for grilling meat and found the foldaway gas grill on my old cooker much more effective, but it's almost impossible to get gas grills now in modern fitted kitchens.