You don't have to pay to change an old driving licence to a photo one. Just get a form from the post office, get a passport type photo, someone has to sign the form to say they have known you for some time and send it off.
One of my sons old driving licence was so awful that it was illegible and, in any case, he'd changed addresses about 10 times (he flits from flats to flats) since it was first issued. We thought in those circumstances we would have to pay, so sent, not only an adoption certificate, but also proof of current address and a £20 cheque. He received his new driving licence and the cheque was returned.
I know when my OH and I moved, we "innocently" sent off our driving licences for change of address and got a form back telling us to get photos. We duly did that and just sent the whole lot back and got our new licences.
Just try it.
Lizzie