There is no time limit on indefinite leave to remain, but it is automatically invalidated if you leave the UK for more than two years. ILR may be revoked if you commit a serious criminal offence. If you have accidentally overlooked the expiry date of your BRP with indefinite leave to remain endorsement, this does not mean that you have lost your right of residence. However, it is advisable to apply for a new document before the expiry of the previous one – such as 3 months in advance of expiry.