300tdi remote locking or not?

I bought an M Reg 300tdi but it didn't come with a remote key fob, but it does have central locking, the guy said it never had one when he bought it.

Is the fob missing or did some Discoverys not have remote central locking as standard? If the fob is missing, can I get a replacement? and does it mean it has an alarm somewhere and immobiliser?

Another thing... when I unlock the passenger door, the other doors don't unlock. Is this usual?

Thanks guys.