A registered nurse (?theoretically a first year RN) gets paid 29 per a hour (more than an FY2 and marginally less than ST1/2)
I think you are confusing Registered nurse and Newly Qualified nurse.
Registered nurse just means that she is indeed a nurse (as opposed to an old system when there was enrolled nurses and staff nurses), regardless of her experience. A newly qualified nurse is a registered nurse as well but she could not work agency and certainly not for Thornbury.
I am a registered nurse, with 32 years experiences, when working bank, I get pay 14 per hour, when working agency, I get pay 23 per hour, which is much more than what the NHS pays indeed (my daughter who is newly qualified and work for the NHS get pay about 10 per hour).
And of course I "can" canulate or do other simple skills, but when working agency I don't have the right to, because hospital policies in UK regarding nursing practice, are extremly heavy and frankly quite absurd.
Thornbury is a very specific "last minute agency", who provides specialist nurses (ie ICU or A&E), on a very short notice. They are notoriously expensive and all ward managers try to use them as a very last resort. As a result Thornbury nurses usually don't rely only on this agency but they are usually also employed by either the NHS or by other much cheaper agencies.
If you work with so many agency nurses, they would probably be happy to explain you all that...