No you can't. Under the Gas Safety (Installation and Use), Regulations 1998, legislation dealing with gas appliances and installations came into force (31 October 1994, amended in 1998).
By law, anyone carrying out work on gas appliances or fittings must be competent and registered with CORGI (Council for Registered Gas Installers).
Please don't even think of doing this. It shouldn't cost too much, but even if it does it's not worth risking your life for. A poorly connected cooker could be lethal. Look in Yellow Pages for a CORGI registered fitter.
As jannieannie said...if it's just a matter of connecting it to an existing fitting....which should be a bayonet fitting, it's just like changing a light bulb and can be done easily and legally.
NO. Once you have fitted it how are you going to test it to make sure there is not a fault with it.??? Just because it is brand new does not mean to say it has not suffered a knock or anything else and could be dangerous. And also it will have to be notified as a new installation anyways and only a CORGI man with a CCN1 & CKR1 training can do this.