Becky,
Any employer that has multiple sites with even a moderate number of employees in the UK will have an equal opportunities policy. I would suggest that in your conversion you ask the question along the lines of; "In my interview you asked about being comfortable working with gays". "What's the company diversity policy statement on this and how do you monitor it?" "Will this impact upon any data we collect i.e. customer feedback, or monitoring our equal opportunities status". This is job specific stuff for you.
This should give you a feel for just how seriously the company takes these issue.
I would suspect that without stereotyping as an industry it attracts many at the more femme/liberal end of the gender spectrum. As others have said give it time and suss out the "corporate culture". If you find someone in the higher management you feel you can confide in the broach the subject. They may say yes dress as you like, it's ok or they could say no as it could effect our supplier/customer relations; we have a "dress" code.
