I'll share my experiences:
Contact was via this online form. You get a confirmation email that your message has been receieved fairly quickly, and then get a reply later. Each successive reply comes in with a different subject line (basically a reference number seems to get added) which messes up threading somewhat. Although it's not on their web site, I assume the email address works directly instead of via the form.
At one point they asked me to continue the discussion via a secure communications channel. This seemed like a good idea, other than the fact they're secure form doesn't accept special characters, which includes apostrophes and limits your message to 750 characters. If you put apostrophes in, it just says "You have not completed all required information" and gives you no indication of why it hasn't accepted your message.
Bank Of Scotland
Unfortunately, Bank Of Scotland don't seem to want you to email them with general enquiries and say you need to be registered and log in to send an email to them. Disapointing, especially given that even they say on that page that you can discuss non-account specific information via email. So why not open it up?
To be fair, Bank Of Scotland were the only organisation where the exchange of emails threaded properly in my mail reader, which is a great help for records.
Email address provided on their 'Contact Us' page. Nice and simple. However threading of emails didn't work though for some reason.
They have a contact page that you fill in to send details to them and they reply via email.
This sounds good, but in practice you get an email back with a return address of firstname.lastname@example.org, which you obviously can't reply to. In my case they failed to answer my question and on the second attempt (for each contact attempt I had to submit another request on the contact page) they emailed on Friday evening to say they'd call me back, and I've heard nothing up to the following Wednesday. Sent another request through the web site to complain about not getting a call. They called on Thursday when I wasn't at the phone and left a frankly unintelligible message. I sent another request, and got a call back on the next working day where I was able to discuss the issue with a representative who appeared not to have read my previous communications. Overall, a bit more work than it should have been.
I tried to find a way to contact them, but like Bank Of Scotland, it wasn't possible without having an account with them.
Very similar experience to First Direct, although finding the email address was more tricky. It was findable through their SecureCode FAQ which is on the external securesuite.co.uk site. Again like First Direct, threading of emails didn't work as expected.
They made it easy, with a direct email address on their contact page
Visa also makes it easy to contact them via email via their contact page. They also were the only company I contacted which included the history of the conversation in their replies, so I didn't have to go back to remember what I'd said to them, which was useful given that they took a few days to reply :)