I just bought a 2002 cooper and the passenger door doesn't open with the central locking.

It locks ok, and can be opened ok with the handle inside.

Bit of a pita tbh so can anyone help out?

Hi there
It seems to be a common fault on these - I think you'll need a new lock mechanism for the passenger door. I tried ebay for a second hand one but they wanted nearly as much as a new replacement from my local BMW dealer.
Unless you can get it much cheaper i'd go for a new one from the dealers.

It also may have been set so you need to press the unlock button twice, one press opens the drivers door 2 opens the rest, in some countries it has to be like that, but i think it can be optionally set by the dealers on any car