c

an agreement under this section [to which an owner or limited owner of land or a trustee acting under paragraph (b) is a party] may be recorded in the General Register of Sasines or (as the case may be) registered in the Land Register of Scotland and, on being so recorded or registered, shall be enforceable at the instance of Scottish Natural Heritage against any person having an interest in the land and against any person deriving title from that person:

Provided that such an agreement shall not be enforceable against any third party who shall have in good faith and for value acquired right (whether title has been completed or not) to an interest in the land prior to the agreement being recorded or registered as aforesaid, or against any person deriving title from any such third party;