Hi there Persephone,
Yes, this does happen, although I suspect rarely now. I remember a good 8-10 years ago having exactly this, one account and a Visa card and a Mastercard on it.
I have a feeling it's for people starting out with credit cards so not just new immigrants into the UK, but all people who are 'starting out' as it were.
I haven't really come across it much since my accounts got upgraded after having this type for a little while.
It's nothing to worry about as such, just be careful not to use them both willy nilly!
Cheers, DtM! West London & Slough UK!