Does CoinBase and or BitPay handle the British Pound?

I think the reason is both legal and the ability to convert the currency to the company's country fiat. Make no mistake these companies accepting BTC are not holding BTC.
This. Although there are a bunch of exchanges that let you use a wide variety of currencies, there aren't many (if any) mature payment processors that convert to something other than USD. There needs to be a pound/euro/etc payment processor that plugs in just like visa/mastercard/paypal that is mature enough for a big company to trust.
It would not be difficult for a european merchant to convert their dollars to euros if they were to utilize coinbase for bitcoin payment processing. Even if they were not able to do so, there are many international companies that have a legitimate need for dollars.