Any reason my car would suddenly start consuming at loynmore diesel?

Geodark

Diesel is always less economical in the winter. As well as this, when was the car last serviced? including fuel filters etc. Is the car reaching temperature? are there any warning lights on the dash? have you been making shorted journeys? Have you been stuck in traffic more? There are many reasons a car can use more fuel.

Ant555

I know i'm late to this thread but I recently got my glow plugs changed Corsa 1.3 diesel due to a code/light on the dash which I ignored for 2 months - and although I admit there might be a placebo effect but the performance difference was immediately noticeable as I was driving away from the garage and remained so for quite a while.
(It wasn't the red engine light but a yellow spanner light)

Im more used to it now but to my mind it definitely made a difference and the fuel seems to be lasting longer too.

So, not scientific analysis and I know you dont mention any dashboard lights but I wonder if it could be glow plugs - someone at my work said that my car computer might have gone into a default mode caused by the glow plug error and this reduces performance and fuel economy to protect components however, I am perfectly willing to be corrected on that.

hope this helps.