Engine knock?

few hundred miles since last oil change
but just had brake pads changed

you kind of answered it your self the motor is locked up. it probably leaked oil out from maybe something hitting pan and draining oil out or it had been going bad like a rod bearing for a long time.

Would that make a sound before it broke?

yes you said it was knocking prior to lockup. you can try turning it over by hand. it could be the cams have locked and not the bottom end, but just from your description I think its' something else. Of course you can always have it looked at by a local pro

No it knocked once then died

if the motor doesn't turn over with the starter then it should be tried to move backwards and forwards as it can be anything like a bolt binding the motor from a torque converter to a rod frozen. have a local pro look at this because it needs to be physically looked at to make a better diagnosis

Ok I have another question
Being as my oil light is on would that cause a no start?

see if your engine will turn over by hand, I think your motor is locked up