In general, a cooking appliance does not require RCD protection since it is classified as fixed equipment and normally the only way such an item could cause an electric shock due to an earth leakage fault is through the metal bodywork becoming live-in general this protection is achieved through good earthing and therefore rapid disconnection with the overcurrent devices ie fuses/MCBs.
However if the cooker control unit has a 3 pin socket on it then it is strongly reccomended you put the circuit on the RCD side of the consumer unit (assuming you have a split load board) (since it could be classified as a downstairs socket capable of supplying outdoor equipment which requires RCD protection)-either that or replace the control unit with just an ordinary 45 amp switch. The latter choice would eliminate the need for RCD protection.
The method of earthing your home uses could also be an issue however regarding RCD protection.
Also, I gather a lot of the time it is very rarely an oven actually requires a 40 amp MCB. (more usually around 32 amp)
I presume that you are asking because you have a split level board and don't have a TT supply with your own earth rod? If you did have a TT supply then everything would need RCD protection.
Also if the circuit will have a socket on (eg an oven switch with integral socket) and is on the ground floor then it is regarded as possible to use for outdoor equipment and needs an RCD