You should try and keep important documents like your passport and BRP safe whilst travelling abroad. However in the unlikely event that this goes missing you need to do the following:
1. Report the loss of your BRP to the police and obtain a police report (translated into English);
2. Report the loss of your BRP online to UKVI using their form;
3. You will need to apply online for a single entry visa which replaces your old BRP. The current fee for this is £154 and can only be used once within a one month period;
When completing the online form you should select the following:
Reason for visit: Other
Visa Type: Others
Visa Sub type: Replacement Biometric Residence Permit.
As part of the application process you need to ensure you provide your passport, police report (translated into English) as evidence that your BRP has been reported as lost or stolen.
Important note: Once you have used the single entry visa to enter the UK, you will need to contact us and inform us.
In addition to this you also need to apply for a BRP Replacement within 1 month of your return to the UK, failure to do this may result in a financial penalty of up to £1000 or curtailment of leave to remain.