Normally you would expect a domestic lighting circuit to be rated at 5A-6A at the fuse board.
A socket circuit would again normally be rated at 20A-32A.
If you install a double socket or even a single socket on a lighting circuit, you are going to create loading problems and very likely experience energy/power loss.
So you must extend and existing socket circuit or create a new circuit.
Cable must follow the permitted safe zones and the new cable if buried in to the fabric of the building, will likely require RCD protection, but excluding that the socket definitely will require RCD protection.
To add to the above, even if you tried to connect a socket to a switch point on a lighting circuit there is a distinct possibility that there would be no neutral at the switch, some socket would not function and a possibility depending on age of property and competence of installer that there is no earth at the switch, thus making it dangerous and non-compliant to regulations to have a socket installed to it.
Best option is to extend an existing socket circuit in the house, if no RCD protection exists on this circuit fit a RCD Fused Connection at the supply socket and extend externally. If you have RCD protection fit a double pole isolator at the existing socket then extend from there.
You must make sure, if the circuit is a ring final circuit that you have not taking the feed/supply connection from a unfused spurred socket.
legally you would be required to prove the work you are doing is safe, both during installation and prior to commissioning.
My question to you, would be how do you intend to do that?