Not my workplace as such, but I used to volunteer for a charity which briefly had an office in this building:
http://www.bellsfarm.org.uk/
I think the council may have owned it at that time or some charity, so the office space was free of charge ad we were thrilled to have it. We had a monthly meeting in an upstairs room there - we got the office space later. I think I have posted before about the night when some of us stayed behind after a meeting. We had the keys and had been shown how to arm the alarm system. This was probably around 20 years ago. A person working there warned me that other groups had been locked in, and that there was a female ghost in the building this person and others had seen. She liked men and children and disliked women. As we were an all female group, we were told to expect 'something' might happen. The person who worked there wasn't on the premises at night in those days, and so we were expected to arm the alarm system and lock up and leave.
When we came to leave - which we had done before with no problem but IIRC this meeting went on longer than usual - we realised we were locked in. We couldn't get out of the fire door for a reason I forget (set off the alarm?) By a total fluke, one of our members was married to a locksmith so she rang him and he came out and had to 'rescue' us. He couldn't explain it either. It wasn't too scary as there was a few of us, but I'd have been terrified if alone or with just one other person...
I happened to be into living history at the time and was told a group of re-enactors sleeping there overnight had some weird experiences - some of the men were goosed (and no-one was that close to them!)
I will be honest and say every time I approached and left, I always felt like I was being watched and from a certain window. We all talked about it openly after a while and I wasn't the only one. This window was the room where we had our committee and other meetings.
I had to be in the office alone quite often but in broad daylight and with other workers/volunteers in the building, but I was still really scared. It never felt 'right' somehow and whatever it was felt malevolent.
Looking at the website I see viking re-enactors still meet up there so would be curious if they have had any experiences. I know someone who worked there claimed to have seen a female ghost and at pretty close quarters if I remember right (can't recall if more than once and I don't want to say owt to identify this person although if you ever read this, would love you to recount what you saw).
I never actually saw her but a good half dozen of us had the experience of being locked in, that night and I know we weren't the first. It was strongest in that room where we met (not our office).