Pre-paid, pre-addressed Lab-Return bags with Royal Mail Tracked-24 postage. 1-2 Business days (MON-FRI) to arrive in Lab.
You must make sure to find your closest Royal Mail Priority Postbox and post there, not a regular post box.
This is the minimum requirement for UK Government Day 2 and 8 Tests. It means your test results may take several days, if posted on a Friday or Saturday to get your much-anticipated clear result!