New Presidential Guidance is out on taking oral or video evidence from abroad. Following Agbabiaka, permission from the foreign state is needed. The process now is to provide the employment tribunal details as soon as possible and for them to contact an office at the Foreign, Commonwealth and Development Office (FCDO), which can confirm permission.
In some cases that confirmation will be through prior knowledge of the state's position. In other cases it will be by the FCDO office making embassy inquiries. The latter approach can take a long time, so it's important to inform the tribunal about a foreign-based witness as soon as possible.
If permission is taking too long and might compromise the trial date, the tribunal can look at ways around it including whether evidence can be in writing (including answering written questions), the person can come to the UK, someone else is able to give the evidence or it's not needed.
This is taken from a twitter thread produced by Jason Braier from 42 Bedford Row.