was probably tesco petrol i reckon, its not my car or wasn't my car but probably will be now
do the bent valves move freely, are the guides scored / damaged, where are they bent, near the head or further up the stem?
Good point I hadnt looked at that pic full size and I'm sure you are right. The fact that both exhausts are showing a bit of detachment could have been cause by local overheating again, the head exanding too much as it goes over its design temp . If you bend a valve you can take that plug lead off and limp home, you wont melt all the plastic on the engine. I agree that a new head and you are good to go, that one is scrap.what has happend there (imho) is the valve seat has come out (can happen)
it has dropped out and done a load of damage as the valve hammers it back in
If you look closely there is a space between the seat and head. this would happen as the seat takes chunks out as its been slammed back into its hole by the valve. it might seem ok now (wont come out) as the head has cooled and tightened back around the seat.
used to happen a lot on old brit bikes.