//you have to get a photocard licence when you reach 70 - then renew every 3 years instead of 10.//
In fact, when you renew your licence at 10 yearly intervals all you are renewing is your photocard. Your entitlement to drive remains valid until you are 70 (unless the DVLA revokes it earlier, which they must do in writing). Then it expires and does so every three years thereafter.
There is considerable confusion about this even among police officers. They sometimes attempt to charge a driver with driving without a licence when they have an expired photocard. This is not correct as they still have a valid licence to drive. All they can be charged with is failing to update their photocard. This is a non-endorseable offence which carries a fine only.