It sounds to me that the car has been bodged about by Uncle Albert and the Sunday morning mechanic's brains trust. Get it to someone who knows what they are doing, like an independant Ford specialist and get a professional opinion, it will probably be cheaper in the long run than trying to troubleshoot it yourself.

As unthrottled says, check all of the rubber pressure pipes between the turbo and inlet manifold Splits might be hard to see so maybe use a mirror on a stick to see all sides of the pipes and grasp them and squeeze to open up any splits. Also check all jubilee clips are tight. A leak might be revealed by oily spray, as the air from the turbo contains an oil mist which will blow out of leaks onto adjacent areas.

The short 'concertina' pipes either side of the intercooler (mounted on top of the engine, immediately behind the front crossmember) are pretty flimsy and often start leaking on this engine - I replaced those on my car with sturdier silicone pipework (but needs corrugated section for flexibility as the intercooler is mounted to the bodyshell).

Another thing which happened to my old TDCi was a large loss of power after having suspension work done. Turned out a vacuum hose to the MAP sensor was detached. Check the small bore rubber pipework between the rocker cover and bulkhead to see if they are all secure and not split.