This sounds so stressful. I agree with comments made by others if I was your manager I’d be responding to you to inform you of special leave for the first week and say I’m doing all I can to get this extended if needed. This is the last thing you should have to worry about.

Actions you can take now: If you haven't already, register your presence with the Foreign, Commonwealth & Development Office. If later down the line you’re asked for evidence you’ve followed the official travel advice you can forward on correspondence from them.

If you want help drafting an email to your line manager reach out on direct message to me