I had a similar problem in my last year working for BT in 1994.
We had a new Boss that would spend hours working out what we should be wearing, rather than devoting his energies to more important things, like making sure that the toilets were cleaned very day.
He told us that we should be wearing BT corporate clothing. For us chaps it was a white, 60/40 poly-cotton shirt, like a bus driver might wear and trousers of some unknown hairy material that would have had me in a rash from ankle, to somewhere further north.
I refused and and wore a M+S formal light blue shirt, with a pair of wool trousers from their mid-priced range. This wasn't good enough for our Little Hitler. When I queried why he expected us to wear this ridiculous BT uniform, designed by someone called Klein.....not sure which Klein, Roland I think, or Patsy Klein perhaps, when we were in an office 10 stories up in the air, where nobody but ourselves would see us. ie we were not "customer-facing"
An answer was not forthcoming, just more guff. I continued to refuse to be bullied, although some of my co-workers buckled under.
I left BT at Xmas that year.