This cuts both ways of course: you can make money on favourable currency moves. But it's an important risk to be aware of before buying assets in a foreign currency.
If you spread your investments in many different currencies in pound terms you would have actually gained from this crisis.
Diversification also applies to currency
A US investor who bought foreign assets in 2014 and sold them today would have been hurt by the 25% USD/EUR rally in 2014-2015. The dollar rose against almost all other currencies too (besides, for example the yen).
I don't normally change the holdings or attempt active investing, but it just seemed like a very asymmetric bet - nearly 50/50 polls, very large potential downside if not diversifying outside the UK/sterling.