If you do want to "go it alone" here are the rules,
https://www.ofcom.org.uk/manage-your-licence/radiocommunication-licences/pmse/pmse-licence-infoBasically you can use any frequency from 863.1-864.9 Mhz UHF without a licence, generally 4 wireless channels is the hard limit or 173.700-175.10MHz VHF. These channels (esp. the UHF ones) are used by many wireless audio devices as it's the only UHF licence free band so is more likely that any other option to get interference.
If more channels are needed then a shared user licence is available, this allows the use of CH38 (or there are some VHF channels available for a separate charge) and Ofcom reckons up to 10 wireless devices (channels) can be used, though these are usable by anyone, anywhere with a licence, so naturally interference could be a problem.
Lastly there is a fixed site licence. This is a coordinated licence that allows specific frequencies to be used outside what is available on (the sliver of) CH70 and CH38 on a case by case basis at a specific site ONLY, these are available for as little 15min and are coordinated so as not to interfere (in theory) with other users, Ofcom will support instances of interference on this channel.