Hi; I bought my tdci ghia estate from new in 2003. Up to 70,000 miles the best I could achieve was 43 mpg! I complained to the local Ford garage and they said there was nothing wrong (at the time I was getting 39.8 mpg!!!). When the car started misfiring a few months later, it was taken in to a different Ford garage, who reset the ecu(?) or computer thingy(?) - since then, it's achieved 45 mpg regularly, and now, at 90,000 miles, it's up to 47 mpg. This is still considerably below the 52 mpg that a work colleague regularly gets. I try not to drive hard and my journeys involve long periods of 60 mph cruising. I think that the consumption seems to vary from car to car - it shouldn't, in this day and age, but I appear to be stuck with it.
The glow plug warning light isn't necessarily telling you that there is a glow plug problem. It simply is telling you that there is an engine problem of some sort - could be serious, could be minor. About once a year this light flashes on my Tdci, and it usually means that the ecu(?) is playing up. Sometimes the local Ford garage have told me to switch the engine off, wait a while , and then restart the car; this resets the ecu and the engine works as normal. On other occasions, this doesn't correct the problem and I've had to take the car in, and they have found that there have been a number of "fault codes" over a period of time (their diagnostic computer reads the on board computer thingy).I would suggest you get the car to a decent garage, where they can plug it in; the diagnostic 'pooter should instantly tell them what is wrong. Hope this helps. :)