It's also not as if the pound is a particularly weak currency like the French Frank or the German Deutsche Mark was.
The Deutsche Mark was famously stable and the biggest official foreign exchange reserves after the dollar, it was much stronger than the pound sterling.
Uber was bleeding money for years, they were not profitable until very recently. How would a competitor be profitable if they exploit their drivers less? Especially because Uber only had to fight Taxis, a competitor would have to fight Taxis and Uber