Maybe they knew that fuel duty actually went up on the 1st....
If that were remotely true then the average family would be massively better off than they actually are. A £735 increase in VAT paid would require something like £34k spent on standard VAT rated goods, rather unlikely given that mortgages, most food, children's clothing, gas & electricity, etc are not affected by the increase. Halve that figure and you're somewhere in the right ball park.