If you are able, I would listen to the OBOD podcast (I think it's 42) where Damh interviews someone from the TDN.
From what I took from the very interesting interview, Druidry is still whatever you perceive it to be - a belief system that sits with your own religious beliefs, or a religion in its own right (and there are large separate threads on that nugget). Charitable status was given to the TDN based on the information that it supplied to the Charity Commission, which they have now included into their rules so that if another Pagan/Druid organisation (say The Cheesepuffologists* to use a trivial example) could also gain charitable status if their constitution matched the TDN.
The complication (as I see it) is that the TDN, like the Pagan Federation, provide an umbrella to a number of pagan organisations - some of which do not have strict constitutions that would meet the Charity Commission rules (such as OBOD I believe).
It is a very complicated point of law (which is why it took four years) but to me highlighted that outside of rules regarding financial benefits, no-one has managed to define what a religion actually is.