Investors are also fretting about Britain's negotiations with the European Union over a trade deal and whether a UK budget next month will include much more spending, which many investors say is necessary to boost economic growth.
"While country-by-country tallies of COVID-19 shows an un-alarming total of 15 in the UK, its near 5% current account deficit means a tightening of financial market conditions leaves currencies like the pound vulnerable to the downside," MUFG analysts said in a note.
Sterling skidded to as low as $1.2760 in late London trading before recovering to $1.2775, down 0.8% on the day. Versus the euro the pound dropped to as low as 86.08 pence. That was the weakest level for sterling since November and means the pound has erased all of its gains made in the run-up to the British general election in December.