So my beloved 2.0 TSI SE L suddenly has a huge thirst.

The daily commute has gone from late 40's early 50's MPG, to mid to late 20's MPG.

No fault codes.

Tested at garage and EGR, O2 sensor, Air Con, Secondary Air con, Evap Emissions, Catalyst heating and operation all within normal parameters.

Tyre pressures all good.

Brakes not binding.

I haven't changed my route to work or changed my driving style.

Fuel used is still Tesco Momentum from the same garage.

I'm starting to think laterally, like could it be something the engine drives, like the water pump or alternator causing drag?

Could the MPG-ometer be faulty? (I need to test this next fill-up.)

Slightly baffled, but enjoying the challenge of a mystery fault.

I'd like to find the problem now, before anything catastrophic happens.

Anyone got any suggestions as to vectors of attack on the problem?

Don't trust gauges, use the fill at the same pump every time to keep the car as level as possible. Record the milage before filling and fill with the same amount or until the pump shuts off.

I had a diesel Focus that showed fuel consumption and it showed an average. Same work run different traffic conditions higher consumption!