The person on the phone said that it would appear that you can no longer convert a brown licence to a uk part 21 licence!
Whilst the process (as submitted to EASA) for conversion of UK national licences, ratings, and certificates to EASA Part-FCL equivalents can be found in CAP 804, unfortunately this does not apply for conversion from UK national to UK Part-FCL. Due to lack of foresight, it would appear that an equivalent process for conversion of UK national licences, ratings and certificates to UK Part-FCL equivalents has not been created.
ifitaint...