Same here - spark plugs as well... Ended up with misfire on one cylinder and a limp mode break down. Grrr. AA guy reckoned they were heavily carboned (the spark plugs) due to oil burning. Others say that's usually because it's running rich. Getting it looked into soon (and hope it's not the dreaded piston rings issue). One recent thought, did we all panic with E10 fuel and go too high with the octane level fuel? Saying this as most other cars I see with blackened tail pipes are often performance cars.
Mine's a 59 plate A3 1.8T Sportback, btw. Cheers:)