From 2012 through 2018, the British pound (GBR) has been worth $1.35 to $1.75 in U.S. dollars (USD). Some confusion exists as to why the British pound is consistently stronger than the U.S. dollar despite the United States having a stronger and more powerful economy than Great Britain or the United Kingdom. The simplest explanation is that the nominal value of a country's currency and its economic strength have little to nothing to do with one another. For example, Japan has the world's third-largest economy as measured by gross domestic product (GDP), over 50% larger than that of the United Kingdom, yet as October 2018, it took close to 112 Japanese yen (JPY) to equal one U.S. dollar  and 147 yen to exchange for one British pound .
Nominal Value vs. Relative Value
The nominal value of a currency is relatively arbitrary. What matters is how the value of that currency changes over time relative to other currencies. For all of recent history, one U.S. dollar has been worth less than one British pound. However, as of October 2018, the pound is sitting around $1.54 to one pound, down from $1.71 to one pound in July 2014 . This trend is indicative of deteriorating economic conditions in Great Britain combined with an improving U.S. economy.
It's also worth considering that many more dollars are in circulation than pounds. As of 2018, nearly 1.7 trillion U.S. dollars were in circulation . By contrast, the total pounds in circulation came to a mere 69 billion . To draw an analogy, the 2016 market capitalization of Berkshire Hathaway Inc. (NYSE: BRK.B) was much lower than that of Microsoft Corp. (NASDAQ: MSFT) despite Berkshire Hathaway's share price being much higher. This is because there are many more outstanding Microsoft shares than Berkshire Hathaway shares.
Consequences of Brexit
On June 23, 2016, British citizens went to the polls and voted in favor of a referendum to leave the European Union (EU), of which the country had been a member since 1973. The "Brexit," or British exit, came about as a result of a populist movement that had grown weary of ceding control of laws and regulations to outside forces in Brussels and feared the effects of what it viewed as unchecked immigration into Britain. Economists, most of whom were confident that Britain would vote to remain in the EU, warned of economic consequences that would result from Brexit.
The vote in favor of Brexit, which shocked oddsmakers and roiled world markets, had an immediate and pronounced effect on the British pound, which declined in value by over 8% in the 24 hours following the vote. This is another example of relative value trumping nominal value. While the pound remained stronger than the dollar in nominal terms, investors still abandoned the currency, citing its precipitous decline in relative value.
The pound had a turbulent year in 2018. It began the year as a leading currency in terms of performance but the effect of Brexit negotiations and a weak economy in the first quarter saw it fall to $1.335 against the dollar , the lowest level since December 2017.
 https://www.telegraph.co.uk/financial-services/currency-exchange/interna... (see fourth para.].