Your existing licence will only expire if you do not complete your medical standards test when you reach the age of 45 or if you miss one of the obligatory medicals; it’s mandatory that all HGV drivers undertake a medical once every five years. If you do lose your entitlement to your licence through one of these causes, however, you simply have to complete a medical and send off for your licence again. Under the current rules, the DVLA will issue you another licence as there is no time limit.
https://www.surreyandhampshirehgvtraining.co.uk/index.php/can-reapply-lapsed-hgv-licence/
