Ton up no lights

Davey, you’re still a nutter.
Night you finished your exams
no waiting for the results
drove your brothers’ car
ton up no lights
on the M4 past Bridgend
went to a party, dancing, lost it
wandered out into the woods
lay down and it was there
in the early morning sun it hit you
Gwell yw ystafell os tyf—
this is the best, you thought, it’s the best.
Whose car? What keys?