Hi,
As i had lot of trouble with my Audi a4 DPF getting blocked i thought of helping others who have same problems.

Here is the solution

1) Take the car on a road where you can drive at 50mph for atleast 5 to 7 mins. Drive continuously for 5 to 7 mins at the sppeed pf 50mph in 4th gear at or above 2000 rpm. My audi clears in 4 mins (Continuous means ,do not apply brakes or reduce speed or let the rpm get lower than 2000 rpm for 5 mins) Achievable in motorways or dual carriage way.

2) Always Full the tank with diesel as it helps alot. Once you clear the dpf you shouldnt get problem till the next refill.

3) Do not ignore the warning light of dpf blockage, take the car on a long road as soon as possible annd follow procedure otherwise engine management light would come on and car would go in limp mode and would not gain a speed more than 40mph and would need to go to audi for forced regeneration costing 130 pounds.

Hope it will be of help
for more info visit following website of AA explaining what DPF is

diesel particulate filter (dpf) | AA