Changes in exchange rates are predominantly the result of market sentiment, the assessment/feelings/mood among dealers, buyers and sellers, sometimes causing very short blips. Fifty years ago the Pound was worth around USD 2.60, now it is worth half that. In 2000 the Pound was worth EUR 2.37, now it is worth half that. It seems the world reckons the UK economy has performed half as well as others and that compared to other currencies the Pound is uninteresting.
Not to worry, we are told that the new dawn heralds unimagined recovery and very likely boundless prosperity - maybe to the pre-1975 levels when the UK was "the sick man of Europe". Ah, I remember it well and how good those days were (not).