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I had the head refaced and new valve stem seals. Refitted using the timing tools, but as soon as I started the car it was running roughly. Stripped head off and asked the head refurb company to look and they said one exhaust and one inlet valve were bent.

I am sure I checked the timing after it wouldn't start and it hadn't jumped.

So I am miffed and have the head ready to refit, but I'm worried as I can't understand how I could have bent the valves first time.

Anyone have any possible causes?

Thanks

Possibly one or both of the cams were rotated with the head sitting on a hard bench surface causing a valve strike into the bench? I was told to find cyl 1 TDC then take it back down from there to get the pistons at a safe clearance from any protruding valves during the head fit up - maybe that??

Maybe. If anything I'd have expected cylinder 1 to be bent as when at TDC 2 and 3 are well down in the block if it had happened when fitted.