that your mail did not go out was really good.
i learned in situations like this not th act to fast. consider some days and dont do anything on your first reaction.
i dont know britan law but in germany it would be clear. if it is a registered trademark and it is in the domain they have the right to take it from you - no matter if it is .nfo or whatever. that ia why they use trademarks

.
in your case it seems not sure if they have the right for a domain related to them. If the domain contians there trademark then its bad for you.
The question is what you can loose. What they do to get it back and how much it will cost you when loosing this. you have to pay there lawyers? court fee? where is the court stand?
So first you have to find out if what you have is trademark protected or not.
If it is i would give it up because it is not worth it.
If it is unclear and you like do deal then there is the chance to get some money.
You should remove adsense. because it contains links to there opponents - even if you cant controll it - but if the play hard they can sue you for not earned profits because of your links to oponents.
If you want money for it then i would put it somewhere for sale. Like digitalpoint where you dont have a price to put in. An then mention on your website with a link to your auction that the site or domain is for sale.
And then see what happens .....