Replace it online
You can apply online if you live in Great Britain, aren't disqualified from driving, and your name hasn't changed. It costs £20 and your new licence should arrive within a week.
Replace your licence on GOV.UK
Replace it by post
Use form D1 from a Post Office and send a cheque or postal order for £20. If your name or address has also changed, apply by post and include the documents showing the change.
If it was stolen
You can report the theft to the police and keep the crime reference. Watch out for signs of identity fraud, since your licence shows your name, address and date of birth. If you're applying to replace a licence that's due to have its photo renewed, you can do both at once.
Your learner journey can carry on while you wait — keep revising for your theory test.
Questions
Can I still drive without my licence card?
Yes — losing the card doesn't take away your entitlement to drive, as long as you apply for a replacement. Keep your application reference handy.
I found my old licence after ordering a new one
Your old licence is cancelled once the replacement is issued. Send the old one back to DVLA.
Do I need a replacement for my theory test?
Yes — you need your physical photocard to sit the theory and practical tests, so replace a lost licence as early as possible.