If you are paying an SP to go with you is it a punt or a swingers party?
The boundaries can be blurred.
(a) You can have a pure swingers party (say at someone's home) where like minded couples attend and there is no financial arrangement and the participants are usually all genuine couples.
(b) Then there are the swinging venues where the owners/organisers charge admission or membership fees but none of the participants have any financial gain although occasionally some of these clubs may pay SP's to attend. It is still classed as a swinging event.
(c) Then there are the purely financial organised sex parties which involve an organiser who hopes to make a profit together with all the female participants who attend having been paid by the organiser. The profit comes from the punters who all pay to attend. This meets all the UKP criteria of a sex party punting event.
In the case of the OP this would appear to fall into the category (b) where rather than attend as a single male, he has a seperate financial arrangement with an SP to attend with him.