1.6 TDI mpg drop over the last 12 months

Hi,

I wondered if anyone could share any ideas as to why I'm seeing a reduced mpg, or anything I've missed that I need to address. It's a 2010 Octavia now with 125k. It's 'unfixed' and doesn't have the dreaded software update.

Firstly, I'll point out I do a lot of trips to Cornwall, 4 hours at motorway speeds, and I'm comparing my mpg to what I was seeing last year, running on winter diesel.

Previously I'd run there and back on a tank, 530 miles, low 50s mpg indicated (up to 60 if travelling slower).

Now, low to mid 40s at same speed, trying to be frugal on acceleration.

So, constants:

Same fuel, Tesco or Esso. Doesn't appear to make any difference.

Tyres, all the same brand, same as last year. Goodyear's. Pressure slightly on the high side with 16". Probably more tread on the tyres this year.

Serviced every 10k, clean air filter (oil is maybe a different brand but vw LL spec). Maf sensor recently cleaned. Fuel filter changed 15k ago.

Speed, I'm driving at the same speeds, between 70 and 80 indicated. Trying not to hammer the hills.

The instant read out when on the flat maintaining speed used to be around 70-80 mpg, this now appears to be around 50.

Wheel bearing or binding brakes maybe? (Front discs and pads replaced circa 6 months ago, didn't seem to affect mpg). 

Did hear a couple of noises when turning left, maybe felt more like a diff binding than a wheel bearing though?

No injector nasty noises.

I monitor vag dpf to see what the car is doing and it's regening as normal at about 400 miles per regen (egr is disabled on my car, and has been for a long time).

Any pointers regarding the mpg issue welcomed