Fuel economy suffering

[Gubmint Agent]

Firstly, the car's a 2.2 Direct with 56k on it and secondly apologies for lack of formatting in this post but I am at work and the IT is sh*te. Just wondered if anyone can suggest reasons for my suddenly-dropping MPG figures. Previously I have held combined urban/distance MPG at somewhere around 36.5 - 37.3 but this has recently fallen to 34.3 MPG. I re-set the BC1 counter each time when I fill up and the last three tanks of juice have only given me around 33.4 MPG. I did wonder if this was in any way down to using Morrisons unleaded for the first two of these three tanks since my fuel light came on at the 390 mile mark where as previously I'd have made it to the 430 mark before needing to refill. My most recent tankful of reputable petrol got me to 402 miles before the fuel light came on. I have in the past managed to reach 480 miles before needing to fill up (but that was a one-off!) There have been no indications that the thermostat is playing up or doing anything differently and I am not doing any different driving (eg, no more short journeys than normal). Anyone got any ideas?

[MrDerv]

Tyre pressures or recent additional load (owt in the boot?).

Other than that, it'll be engine related. Hopefully someone knowledgeable in the 2.2 will be able to help

[stevoxsi]

Colder weather?

[rushy]

Intake temps can lower the MPG by 1-2 I find.

[m8internet]

Shorter, slower journeys
Lower temperatures

Every petrol car I have had usually shows a drop in the average MPG during December and January
Usually by March it has returned to normal

[rushy]

Check your swirl flaps are working mate. Any loss of power?

[vectra ste]

i would of said lower temperatures plus using your heater more

[Gubmint Agent]

Thanks to everyone who replied; my tyre pressures were a little down on normal but I don't think this was the root cause. MPG seems to be picking up a bit now, so hopefully after the car's had a service it'll be even better.