You COULD do, bearing in mind that if a vacuum cleaner or a fan heater is plugged in, the lights will go out due to an overload trip.
It is permitted to put a 13A socket on a lighting circuit, but this is more often done for a defined and known small load, such as an aerial amplifier in a loft, or a fairy lights plug-in power supply in a porch, where no socket circuit is available and the socket can be clearly labelled, and is unlikely to be overloaded.
The round pin socket for lighting is quite common, though I suppose most householders will not know about them.