My kitchen (installed by MFI in 2005 based on the paperwork we got when we bought the flat in 2007) has a single oven on a normal 13A plug that connects in to a normal socket. No separate isolation switch. I think it's on the same ring as the rest of the kitchen (so that includes a toaster, kettle, microwave, dishwasher, washing machine, fridge/freezer). In 2005 this was all within the regs I guess (who knows, MFI might have used dodgy installers).
I replaced the oven a few years ago, like for like, and wired it in to a plug in exactly the same way. I made sure I selected an oven that was rated at less than 13A because of this obviously.
The above (and the fact that the flat is wired with only 4 circuits, no RCDs/etc) is the main reason I want to get the place rewired[1], but the electricians we've had look at it have said that there's no urgent need to get it done, the cables themselves are in good shape (i.e. not ancient cotton covered things that get chewed by rats), the fuses are correct and the loads on each of the circuits aren't anywhere near capacity.
1. We're sticking money away for this each month as the rewiring itself is cheap compared to the redecoration costs (especially with replacement carpets, and other 'upgrades' that it would make sense to do at the same time).