If someone pays for the right to a stall space at a weekend music festival to sell their products what are the different parties - stallholder and organiser - legally bound to supply in the way of protection from electric shock....
The person renting supplies their own stall structure, awnings, equipment lighting, effectively a sole trader.
The person renting has paid for the organiser to provide a 230V supply at their stall. Does the organiser legally have to provide additional (RCD) as well as basic (fuse circuit breaker) protection at the generator end, just basic protection or is the stallholder repsonsible for providing RCD protection? The stallholders pay a nominal fee for the provision of a 230V 16A supply, and a higher fee for a 32A socket.
Is this a question of contract law (whatever they decide between themselves ) or are there overriding H&S regs?

EAWR89, PUWER98, BS7671 as well as BS7909 would all apply, as may ESQCR as ammended.
The supply to the stall must comply with the appropriate regulations, if that includes an RCD then it must be supplied by the "electricity provider", the stall holder must ensure that their "equipment" is fully compliant also.
This may entail the provision of an Electrical Installation Certificate for the stall, depending upon the complexity.
The "electricity supplier" may need EIC's also for their supply, depending on the origin of the supply.
With the information provided it is not possible to design and specify the requirements.
Contract law would be merely a commercial issue as to the cost of the provision.