The oven should have it's own supply from the main fuse box, (consumer unit). The size cable will depend on the load, generally a 6.0mm cable is used to feed the cooker, with an isolation switch mounted near the cooker, either a cooker outlet or a double pole switch which is correctly rated. The fuse for the load (cooker) should be calculated at, wattage divided by 240, this will give you the amperage or current rating. If the the calculation exceeds 10amps, you should then take 30percent of the remaining wattage and add this to the 10amps.
Of course if you bought the cooker from new the instructions will also advise you as to the correct ratings, or it should do.
I have heard some say that they just use a 45amp fuse or mcb at the consumer unit end, this is bad advice as a circuit that has an over rated fuse is not protecting you or your appliance in a way that it should be, so it's best to get the correct ratings for the maximum protection.
Hope you find this helpful.
