If that's the legal arguement then Survivors Network can say they weren't funded to do this.
And in which case the legal challenge should be against Brighton Council.
This comes back to the problem that because a council through is financial control can arbitrarily designate anyone whose financial bid they like to take on a service that isn't regulated by the known regulator, you cant then tell the funded service provider you must observe the regulator's standard if the funder didn't write that into the funding agreement.
This isn't because I believe it is right, but is about the financial contract between the funder and the service.
I am not sure that a court has the ability to say both the funder and the provider are in the wrong legally. But maybe the court can make some moral statement.
Unfortunately there is no one with political clout to take this up as an issue, and both Women's Aid and Rape Crisis seem to be rish averse in terms of standing up publicly for the standards they expect of their members, but seem to be shy about saying to the public and potential users, federated groups operate under these agreed standards.