https://www.slab.org.uk/guidance/approval-for-an-expert-what-work-is-covered/
Where we grant approval for an expert to provide a report, that approval includes the expert’s costs for giving evidence in court where those costs do not exceed £2,000 (excluding VAT). The notification we send you about this will include the information that the court attendance is included in the prior approval.
Where the expert’s costs for attending court exceed £2,000 (excluding VAT) you should submit a request for prior approval for unusually large expenditure.
Where the expert has prepared a report which has not been prior approved, for example, where the case was privately funded before legal aid was granted or where the report was obtained under advice and assistance (including ABWOR), we require to consider any application for the expert’s court attendance.
The following additional work requires prior approval:
While joint instruction of expert witnesses in criminal proceedings is not often possible, where an expert is jointly instructed by more than one accused, we only require an application from one of the solicitors representing the accused.
We will part grant a request for the employment of an expert where:
Approval for an expert witness
Additional guidance on specific expert witnesses – defence post mortems, drug experts, psychologists, psychiatrists, forensic accountants