Hi new to site. Recently just bought a 17 plate focus titanium auto 1.0 ecoboost. My car seems to be eating petrol, I filled up my tank (dash said I had 450 miles) and drove up to Cosford in Wolverhampton from Portsmouth and back again.  Google says it’s 180 miles one way, I did 70 for all the journey when able and I got back home with under a quarter of a tank. Mpg said I averaged 42.1. Does this sound right? 

I wouldn't say 42MPG is "eating petrol". That's average for mixed driving, the manufacturers figures are very inflated. Try resetting the trip computer as it will have counted since it was last reset, which may have been months ago.

If you actually calculate the MPG for that journey (3/4 tank = 30 litres) over 360 miles then you actually averaged nearly 55MPG, which is about right. Plus 450-360 miles would leave 90 miles left, which again is about right.

the only way to do a proper mpg test is to top tank to the brim. Note the mileage. use the car until nearly all fuel gone. fill tank to brim again, note how much you put in the tank this time and note how many miles you did since previous fill up. work out mpg (1 gallon = 4.54 lites). There is no other way that can tell you anything near the accuracy of doing this.

Sweet I will give this a try, now to find the money to fill the tank again 😂