This is remarkably odd, for a number of reasons, but, read into it as you will...
Having never heard from nominet in any form, yesterday I received and email:
I my view, there are several points: Firstly, that an individual is not allowed to sell a domain (even though the domain is not up for sale) Secondly, in the short term a domain may not be parked. Thirdly, even though detail were expressly requested to be witheld, Nominet without seeking clarification and contary to terms and conditions, judged that the long term use of the domain was a parked domain.
Certainly, this is more than a tad concerning.