i just got my fiesta back on the road

and its playing up

, just wondered if anyone knows what it could be.
its a turbo with cosworth management, it was fine for a little while then driving to the mot, i put my foot down and it went well, then joining the dual carrageway i put my foot down again and when it hits boost it starts hesitating and then backfires

. its also using loads of fuel

.
any ideas what this might be...????
i dont know why its was fine one minute then 10 seconds later dont wanna know
thanks