Upon making a successful application for leave to enter the UK, you will be issued with a Biometric Residence Permit (BRP) and required to collect the same within 10 days of your first arrival in the UK from a designated Post office branch. Your passport will be endorsed with a short validity (travel) vignette - which will be valid for 30 days from the expected date of travel provided by you - to enable travel to the UK. You must travel to the UK during this 30 day window and then collect your BRP within 10 days of arrival in the UK. If you need to start work before collecting the BRP, you will be able to evidence your right to work by producing the short validity (travel) vignette in your passport, which must be current. In these circumstances, the University must check and copy the BRP before the vignette expires.
Please read the following leaflet issued by UKVI for full details:
In all circumstances your BRP or travel vignette must be checked and copied by HR the day before you are able to start work.