https://www.gov.uk/driver-vehicles-account
Don't know if anyone has posted this up, but I saw this link on another forum and thought it might be of interest.
I have just registered, pretty straightforward as most of the DVLA website is, nice and clear as to what to do. You seem need a passport regardless, plus driving licence and vehicle V5C for the details.
I registered several vehicles, some needed to have the V5C reference number entered, some didn't, possibly down to slight differences in the way my address is shown or it might be how long since the vehicle was registered to me and a new V5C issued. Whatever, it all worked well for me.
I recently missed a tax renewal when I hadn't received a reminder by post, fortunately I noticed when taking the vehicle for MOT just a couple of days into the new month. Reminders by email and text will definitely be useful to me.