I just checked and it’s only 60 days as well, correctly showing in £s. Same applies if you start from scratch in the store. I just checked the US store and that, too, is only showing 60 days.
You can still get a 1 month sub (renewable if you don’t cancel it) so I’m thinking that maybe it’s not a mistake that they’re restricting gamecards to 60 days. Though it seems odd there’s been no announcement.
/edit OK, there has been an announcement - Changes to Purchasable Game Time Options for the British Pound (GBP)