I am now in the process of changing my address on various accounts (as we are moving house next weekend).
One of my pension providers (Scottish Widows) recently sent me a name/address change form (just in case, I suppose - as I didn't request it) and I held on to it because I knew we'd be moving. I only looked at it closely last night and saw that if I were to request a name change, they wanted me to provide the original marriage certificate!
To quote the form exactly, it reads: "If your name has changed on marriage your original marriage certificate must be enclosed. If you have changed your name for any other reason the original appropriate document must be enclosed, eg Original Deed Poll."
Hmmmm, this reinforces why I am not bothering to change my surname on these types of accounts - I would not be going to the trouble of sending my original marriage certificate off to all these various places, as I've got too many of these such accounts to bother with.