4. An additional fee may be negotiated between the messenger-at-arms and the instructing agent by prior agreement in the following circumstances:
(a)where the messenger-at-arms is standing by awaiting the delivery or uplifting of a document for immediate service;
(b)where the messenger-at-arms has to instruct an huissier or other officer of court outwith Scotland to serve a document; or
(c)where there is no prescribed fee and the importance, urgency and value of the work involved necessitates an additional fee.