You don't need a licensed airfield but you do need approval from the CAA
Happy to agree if you can point to any document that says that.
An RTF does not require any approval from the CAA to carry out training anywhere. And if an RTF wants to train at an unlicensed airfield, all that's required is that the commander of the aircraft satisfies himself that it has adequate facilities. No CAA approval, not even a requirement to send the CAA a copy of any assessment made.
NS