A friend locked herself out of her flat this weekend.
I offered to come round and use my size 11 skeleton keys on it :-) but
she called a locksmith instead.

The lock was a single yale-type lock which locks when the door is
pulled closed.
My question is - how would a locksmith open this?

I thought about drilling through the keyhole with a HSS bit - bit I
guess (hope!) the cylinder should be able to resist this type of
attack?

Mark.