The only series one I’ve been slightly familiar with (not mine) many years ago didn’t have locks that I can remember.
It’s not a marque I’m clued up on to be honest.
 
If you are asking if an aftermarket option is available then there are a few ideas floating about at the moment. A few later series owners fit garage door bolts as extra security.

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Sadly they will require visible alterations to the vehicle that may bother some.
Cheap enough and reasonably secure but I’m afraid I don’t know if the Series 1 door will accommodate them.
 

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