The sterling fell from 2$/GBP to as low as 1.35$/GBP during the past year, and is presently around 1.69$/GBP. So there has been a tremendous devaluation of sterling vs $, making $ priced goods more expensive than before. The second piece of the pie is import taxes and transport. The third is the distributor (PMC's) commission, which appears to be very high, since taking for the effect of the first two items still leaves behind a large unexplained price gap. The net effect is that Bryston gear, which was very expensive to begin with due to distributor commission and import duties, is now even more expensive due to a weaker pound.
British products should have become correspondingly cheaper in the US. If this is not the case, the dealer has decided to keep the additional income due to the weaker rate for himself instead of pass it on to the customer.