Upper tier (CBDU)
For businesses that carry, broker or deal in other people's waste. Skip hire, man-and-van rubbish removal, house clearance and commercial waste firms collecting from customers normally need upper tier. Registrations last three years and must be renewed.
Lower tier (CBDL)
For businesses that mainly carry their own waste, and some organisations that only handle certain low-risk waste such as charities and waste collection authorities. Lower tier registrations do not expire, so you will not see an expiry date.
What this means for you: if a firm is coming to your home to take away your rubbish for a fee, you would normally expect to see an upper tier registration. If you are unsure, ask the firm or check the guidance at gov.uk.