Intended to be lighthearted?
Jeremy Corbyn? Panic would be in his eyes, I fear. Or he might have proven unexpectedly masterful. Who knows?
Theresa May - would make a lot of set-piece speeches from a podium. ("This is the best way, it is the only way." "I have just chaired a meeting of the Cobra committee, and it has been decided...." "Some people call this the Nasty Virus. And they are right.")
David Cameron - I just can't tell?!?!?
Gordon Brown - would be grumpy and on top of things.
Tony Blair - would be saying "I sincerely believe a lot", and being generally icky, but probably effective.
Can't really remember Major and Thatcher.
Of course, if Bercow were still Speaker, he might have declared himself Emergency Leader, under the power given to him by Standing Order 32, last used in 1641 😂