Why on earth is this country so expensive?

Full trolley (till overflowing) of shopping in USA supermarket costs $58.oo (£29.00 equivalent); here that could easily cost £100.00 and more. 3 times more expensive.

This seems to have been a big change in my experience. I was out visiting in laws in the states in February this year and a food shop at a bog standard supermarket is comfortably double the price of a UK shop.