English is my first spoken language but I have an understanding of a couple of others, as well as a good knowledge of sign language (though the chances to put this to use have been rare). It came up in my interview, it's on my CV and I assumed that HR might note this somewhere. We had a visitor to the office recently - let's call him 'Ryan' - who communicated using sign language exclusively. He also came along with an interpreter provided by our company. I was not directly involved in anything Ryan and the managers did before lunch. We were only given a brief introduction.
At our lunch break, Ryan and the interpreter sat with me and we were having a casual conversation. Ryan asked me something through the interpreter and I responded with sign language before the interpreter relayed it. Ryan was at first surprised but politely responded afterwards and seemed happy to continue in such a way afterwards. We both understood each other and I'm confident I said what I intended to say (which was all positive!). Ryan did mention that nobody told him there was someone in the company who could use sign language. At first it was just the interpreter, Ryan and myself. When others joined us, I spoke as well as signed; something often do anyway as sign-users I've met before could lip-read well and if I'm not sure of the sign for something. Later in the day, a manager brought me aside and insisted that if there is an interpreter provided for visitors, we do all our communications through them. From my discussion with the manager, I know for certain that Ryan was not discomforted by the experience, I said nothing inappropriate or incomprehensible, the through-interpreter-only rule is not an official company rule or policy, and despite having to communicate with clients across the globe, HR keeps no record of what languages etc. we each know.
I can appreciate that if this were a formal meeting, I would defer to the interpreter's greater skill to reduce the risk of something being conveyed incorrectly, but this was a casual conversation that had very little to do with our work. I wasn't disciplined as such, but this is the first time I've had to be so sternly warned by a manager not to do something. It caught me quite off-guard.
My question is; in a UK-based workplace, if an interpreter is provided for a visitor, colleague, client etc., is it considered unprofessional to communicate directly to the person(s) that need the interpreter?