Kitchen - ring or radial circuit?

Kitchens are the biggest electrical demand in the home. Electrical Hobs should always be on their own designated circuit; in fact anything above 2KW is recommended be on it's own dedicated circuit (See BS7671 appendices). Suitable and adequate circuit separation will benefit you, as in the event of a fault, the minimal disruption to unaffected circuits is always preferred. Proper design for loading and safety reasons should be completed by an electrically skilled person. Rules of thumb is only used when persons are either too lazy or too stupid to know the correct method.

There's no definitive right or wrong here but Ring mains come with their own problems (ensuring and maintaining continuity of the ring being one of them). Radials are limited to 20a on a 2.5 mm cable so you could get up to the limit reasonable easily in the kitchen (rule of thumb is 1KW = 4 Amps) while a Ring will be rated at 32A. Personally I'd run two 20A radials and have the ovens and hob on one of them, leaving the rest of the appliances on the other.

Run a ring for general sockets. Oven and hob on radial in cable to suit load. If cabling is an issue do radials for your sockets but run 4mm and then you can up the breaker size if you want to. There is no right or wrong. If you are likely to use lots of high power kitchen gadgets at the same time then go for a ring but the chances of ever pulling anything like 20a for a long period is pretty remote.

Every Spark will probably give you a different answer, a cheap sparky would probably put 1 ring circuit it and a seperate circuit for the hob (Electric Hobs should have thier own 32amp supply via 6mm cable) I would do radials in 4mm and probably have a mixture of a ring (possibly 2) main for general use counter top sockets ect including oven, a radial circuit for the Hob and it's worth considering a radial for the fridge/frezzer so if you have issues with the other circuits you won't have to worry about the food defrosting. But this can all add to the cost. A good sparky should be able to advise you on the different ways it can be done and thier advantages and disadvantages.