Expired biometric residence permits (BRPs) can no longer be used to travel to the UK.
You will need an eVisa if you’re on an overseas assignment and you’ve previously been resident in the UK.
Before travelling you should set up access to your eVisa by creating a UKVI account if you have not done it already, and make sure your current travel document is linked to your UKVI account. You should also get a share code before you travel as you may be asked for one.
See the Foreign & Commonwealth pages at aff.org.uk for guidance. If you have problems creating an eVisa you can email fcsupport@aff.org.uk for help.