Like many companies a friend of mine pays his taxes to HMRC via internet bank transfers from this Santander bank account. He has been doing this for years.
The latest payments failed to complete and upon speaking to the bank he was told that the HMRC acocunt number/sort code he is using cannot accept Faster Payments! But, the Santander bank website facility has been upgraded and now only supports the new Faster Payment method. So he's stuck!
I mention this just in case other people encounter the same issue with making payments to HMRC, especially via Santanter. I use Bank of Scotland and that system allows for the traditional "Slower Payment" method!
There is nothing Santander can do about it seemingly.