Five Guys is in the U.K.??!! I did not know that. In the USA their double cheeseburger alone is $6.99 not incl. fries or drink. I like their burgers, but IMO they are overpriced for what you get as are most of the "gourmet" burgers over here with a mere few exceptions. As an example, I ate for the first time recently at the legendary Fuddruckers and paid $12 & change for a 1/3 lb. burger with all the trimmins' , a Coke and a microscopic order of onion rings that would have caused a midget to look askance. I felt like I was screwed w/o getting kissed.
There is a local neighborhood bar in a small town up the road from me about 10 mins. that has a 1/2 lb. burger with a bushel basket of fries and a soft drink for $10 & change that was the best I have eaten in my area, although the last time I was there was a few years back.