SecretLeeds - History, culture and architecture in Leeds

Quite a few years ago, when I worked in Leeds, I used to wait for the bus back to Stanley (number 443) on Black Bull StreetThe stop was outside a large brick building, & by the double(?) doors.The letter-box was still on the door, & if prised open gave a view of what appeared to be a large reception area, & a staircase.What was this building, was it related to Yorkshire Chemicals?

I think the offices on your side of the road were Yorkshire Chemicals and the works were on the opposite side.