It is alot simpler than that and free.
That valid too date is your photo. I called DVLA recently as mine runsout in April and I was wondering what I needd to do.
About a month before you will get a reminder in the post. all you need to do is send in a new passport photo and your old license and they will send another one back all free of charge.
It doesnt matter if digi tacho cards have a different photo on them to your driving license