Despite rule 18 , when a solicitor claims to exercise a lien for unpaid legal costs over client documents which are essential to the clients defence or prosecution of current proceedings (a) if another solicitor is acting for the client, the first solicitor must surrender the documents to the second solicitor (i) if the second solicitor undertakes to hold the documents subject to the lien and with reasonable security for the unpaid costs; or(ii) if the first solicitor agrees to the second solicitor agreeing to pay, or entering into an agreement with the client to procure payment of, the first solicitors costs upon completion of the relevant proceedings; or(b) alternatively, the solicitor, upon receiving reasonable security for the unpaid costs, must deliver the documents to the client.