Having taken apart my old crappy kitchen I have found that my oven
power cable has a plug on the end and is plugged into a normal plug
socket, I always thought that they had to go into a 30amp box, is that
correct?

Most ovens these days come with plugs and only need a 13A socket. However,
if you only have a single ring for the house, or a single ring for the
kitchen, you might find that this circuit becomes overloaded with the
dishwasher, tumble dryer, washing machine, microwave, fridge, freezer,
kettle and toaster. Any fix should look at the kitchen as a whole, to see if
a more equitable split between circuits would make sense.

Christian.