https://www.slab.org.uk/guidance/advice-and-assistance-increases-for-expert-witnesses-based-at-a-distance-from-court-factors-to-address/
It is usually more expensive to employ a medical or other expert who is based at some distance from the court or your client, rather than a more locally based expert. If you seek to employ such an expert, you should provide details of:
Increases in authorised expenditure under advice and assistance and ABWOR employment of third parties
Discover when it is acceptable to trace a relative, party or witness and the implications on the availability of advice and assistance.