Im back on line again for anyone that remembers me... (www.silversaph.co.uk) with another problem

Driving home last night around 70mph, dropped it down to 4th and floored it, got 3 or 4 big bangs/pops/backfires so lifted straight off, tried it again and got the same. After that had no other problems, was it due to the fact i had no option but to put in crap cheap tescos petrol rather than optimax that i usually use?

Help please!