Hi, I know it's a bit late from your OP, but thought I'd chime in!
Most, if not all of the maltings over hear produce a British munich malt. I live about 30 mins drive from Thomas Fawcett's maltings and can pick up from the maltings direct (You wouldn't believe how much a 25kg bag is

) so most of the domestic malts I use are from Fawcett's.
Flavour wise it is completley different to German munich. In comparison to the Weyermann munich malts, which I find to have just an awesome bread crust, light toasty, biscuity quality, the british versions have the same qualities but more intense. I wouldn't use it for say a 100% munich beer like a munich dunkel, or even an Oktoberfest as the british version can get quite cloying at high % rates. That being said, I use it in nearly all of my pale and IPA recipes as it kicks ass as a malt profile booster and adds a subtle complexity to the base malt profile of paler beers. Its pretty popular for such applications over here with both home and pro brewers, and I suspect it would help to boost the US domestic 2 row flavour profile for brewing British style beers.
As a rule of thumb 20% is about the limit most of us use UK munich, although I do know people who have used higher %, I supose it depends on what you want out of it.
Hope this makes sence and can be of some help.
Cheers
LB