If your 30 day visa to work, study or join family in the UK has expired
Posted on the Twitter account of the British High Commission in Pretoria on 6/07/2020:
If your 30 day entry vignette to travel to the UK for work, study or to join family has expired, you can request a replacement visa by bringing your passport in to a VAC, without needing to book an appointment, effective immediately.
https://twitter.com/ukinsouthafrica