Winter driving, the car rarely uses battery power as you need a heater and demister right from drive off so it runs petrol . When asked, most dealers will tell you the claims are not real. If you want to save a tiny amount of fuel or produce less emissions, the extra cost is not worth it. I have used small diesels and 2 litre diesels for 25 years until this year. I found all the 2 litre ones would do a consistent 53mpg overall for 12 months. The 1.6 diesels would do 57 mpg. This assumes no fast acceleration hard braking and keeping under 80 mph. 1.4 diesel would do 60 mpg. My current diesel Nissan is doing 49 mpg as it has an auto box and a largish car shaped like a brick.
One day we will have to accept what they impose on us. I was impressed with the large Mercedes saloon that uses a 1.3 engine and has 160 bhp on tap and do 50 mpg in petrol form. Unfortunately, if you run this at 90 mph it will lower to 35mpg if lucky.
I am experimenting with my new petrol 200bhp car. I anticipate 35 mpg average and 40 mpg on a motorway trip. If it is too thirsty, next change, i will try something different but hybrid would be a fair option having driven a few recently. I did like the non engine running when stuck for an hour in traffic. It crept along on the battery for about an hour as long as i kept the fan and aircon off. These are the problems with hybrids,switch on any high draw electrical items and the engine will be running. Bear this in mind on a dark journey to work with lights on or rain.
Regarding BMW, mine was let down by a main dealer unable to repair or service a new car. I had to take it to a proper BMW dealer in Paignton with proper mechanics that could fit a car radio. The main dealer is on Marsh Barton and one of the largest BMW dealers in the UK. Best service department of any dealer in the last 25 years has been Volvo Kastner. Vauxhall, however had no repairs to carry out at all. It just needed a service and kept going with no faults at all. That one used an Alfa Romeo 2 litre diesel.