IO540, the NATS atco trade union (Prospect) would probably take no interest whatsoever in whether or not instrument approaches were allowed at non ATC airfields. They negotiate our terms and conditions of our employment. There are also other trade unions that represent non NATS ATC staff and I'm sure they wouldn't be that interested either.
The organisation that might take an interest is
GATCO, the Guild of Air Traffic Control Officers (most definitely not a trade union), who like to represent all UK atcos (civil and mil) on professional matters. I am not a member so won't comment on what their position might be any further.
Stop banging on about the union on this subject, I doubt they'll take any notice.