I've had exactly the same problem. I had driven from Mid Wales to Durham when the dreaded Check VSC and limp mode kicked in. Turned off engine and car would run for 5 minutes before dropping back to limp mode. To cut a very long story short, ended up on a 6 hour flatbed journey back home. The usual P2002(particulate trap efficiency below threshold bank 1) alarm was showing when interrogated. After researching here and everywhere else trying to find somewhere near that could do the job, I found these guys - http://www.ecutechtune.co.uk/. These are based in Manchester and even trailer-ed the car up there for me. Have just driven the car 150 miles back, and all I can say is that the car is going better than it ever was. Improved fuel consumption too. So if anyone is looking for someone in the North West, I can recommend these guys. Ask for James. By the way, I had tried all the "magic" additives, but when your car will only run for 5 minutes at a time, trying to get over 3k revs is nigh on impossible. Anyway, damn dpf has gone now, emulator fitted and all hunky dory!