I think you're right, David. Looks like a Series I (1956-58) judging by the chrome flash at door bottom. (Ref. Wiki)
That's a new one on me, Phil, I've always assumed it to be CVH. What other indicators are there to confirm a Sierra one?
I've two sets actually, Peter, but after the battery top up it was fine on a 'proper' battery (condition) tester, so I didn't bother trying a jump. Could bear it in mind if all else fails.