Help! Vehicle tax and V5

I have just sold my car to my brother (private sale). I have just entered an application online to change the V5 over to him. However, obviously he cannot tax the vehicle until the V5 arrives (it says between 5 days and 2 weeks, but I've read other posts by people saying it takes a lot longer). Can he drive the vehicle now? Is there any way he can get the vehicle reference number from the DVLA so that he can tax it now, or does he just need to wait for the V5? The tax I had on the vehicle (as the previous owner) expires on the 29th April.

Thank you in advance