Hi mate seems like dpf /egr problem all diesel cars after 2006 got dpf unless ur has been removed anyway I had same problem cost me 400 to have it cleaned low miles local miles can cause it to block try using v power diesel and dpf cleaner then take it on a motor way in 4 th gear for 20 mins, I had same again used dpf cleaner took on motorway it cleared it, was advised not to remove dpf as lights would return had mine done by car surgeon in Birmingham, give them a call if ur not that far, u say ur tax is high how high??? I pay 205 per yr good luck