Insurance is based on qualified rostered crews correctly mustered for that specific aircraft type and operation. Not on whether or not there 'happens' to be another qualified pilot on board. Odd question to ask and I was referring to the necessity to ask such questions.
Airlines want the money, if they can get away with charging you for 'dead heading' or jump seats you can guarantee that they will. It's free in the US to deadhead or use the Jumpseats, the ludicrous taxes levied against Air Fares in Europe under the 'Green' banner make it easy for airlines to charge for those 'extras'. The UK being the most expensive place in the world, after the recent increases to APD, to fly out of.
Positioning is and always should be a 'duty' hence it is a day at work. If the company 'require' you to operate from a base that is not your home base and they need to get you there by air/ground it is their duty to do so. I think the EASA regulations will muddy this a bit further as they want to allow your 'base' airfield to be within a set geographic distance from your home. (50 miles springs to mind)