Hi Rob - understood and appreciated. An applicant with form OS1 does not have to provide 'proof' with regards the interest, in this case a legal charge, they wish to protect.
However they are referred to the
Warning on the form OS1 with regards misuse and the legal consequences. Your solicitor should refer to that and take the appropriate legal action. That could, merely for example, involve contacting the solicitor acting for the applicant on the OS1 to flag the matter/trigger legal proceedings, which in turn may trigger them to withdraw their OS1
If they have also contacted us then the support team will consider and respond as appropriate
In the interim I would encourage them to submit their own OS1 asap to ensure priority is obtained once the pending OS1 is either cancelled, withdrawn or time expires