If the gas oven is connected to the mains gas supply by a rubber hose with a plug in bayonet fitting then you can just unplug it and remove it. this should be fairly obvious as a twist and remove fitting. I would be most surprised if an integrated oven is connected with a fixed pipe as this would be a very awkward way of installing the oven. If there is no obvious rubber hose then contact a CORGI regestered plumber through word of mouth via friends or family etc or as a last choice look in the yellow pages for plumbers specialising in that make of oven as they may work to a fixed tarrif regarding work carried out to these appliances. The electric hob is easy enough to remove as long as you make sure the supply is turned off when you disconnect it . it should just be a case of disconnecting live, neutral and earth. People like B & Q should be avoided !!