If it showed £188 on the fare explorer page, where you are (typically) offered a number of different flights, cabins and/or dates, that's only ever an estimate, as (IIRC) the page itself says. It's hard for it to be completely accurate because of the vagaries of combining fares and estimating TFC. The firm price quote is that shown on the price quote page after you have selected specific flights, and even then you're still not committed to buying it if it's more than you expected.

However, if you had a firm quote of £188 and that was how much you were told would be charged to your card, and more was actually charged than that, then you would have a valid complaint about overcharging.