The question is a simple one, however the answer isnít.
if the manufacturer has fitted a 13amp 3 pin plug then the loading is less than 13amps for the oven.
And the ignition for the gas hod has a manufacturerís factory fitted 3 pin plug then it only takes 1 to 3 amps.
So knowing the loading we can look at the fuse board and see if the cooker fuse/MCB is over these values then you should be fine, if you are plugging them into the existing socket.
However, we are assuming that the socket you are plugging them into is Fit for purpose. As we canít assume anything, it needs to be tested and inspected to make sure itís compliant with the rewiring regulations BS 7671.
If youíve had your property inspected and tested on regular basis then you should be ok, if you havenít then I would suggest that you have a domestic electrical installation condition report conducted.
You also need to read the manufacturers instructions for installation.
You canít work on the Gas supply : connection to your hob or electrical circuits unless you are a Qualified and registered.
Sorry for a long answer to a simple question.