The figures don't surprise me, its all just a part of the old Rip off Britain campaign. In todays world the likes of BAA won't accept a tender from some smallish outfit who could do the work much cheaper and to the required standard. Nor do they even consider getting in a contract team and managing the work in house. That is all seen as unacceptable risk. Instead they will go through a laborious process of ticking boxes against the tenders they receive. Probably get a special team of lawyers, engineers and project managers to pour over the tenders.
In reality there are only a handful of multinationals that can undertake a project of this scale given the rules that big corporates such as BAA have essentially self imposed on themselves. Even then the company that wins the tender will retender work and sub it out all the way down to the man who does the road marshalling and sprays water to keep the dust down. All aboard the gravy train with each and everyone adding on a margin in the process. Thats essentially how we get to the ridiculous figures these days for laying some concrete.
Now heres one for innovation.... Imagine hiring a couple of super tankers, fill them up with the materials and equipment brought overseas nice and cheap and throw on board a 1,000 workers at £100 a day. Get in some decent qualified people to oversee the work and throw in some hefty early completion bonuses for all concerned. Reckon it would take more than 6 months to lay some concrete? Kick up a right fuss in the process but get the job done and to the required standard.