Why would they have an all British cast?

This Harry Potter dhidi ya Twilight sanaa ya shabiki contains suti biashara, biashara suti, suti mavazi, mavazi kamili, tailcoat, mkia kanzu, mikia, nyeupe tie, nyeupe tie na mikia, suti ya mavazi, mavazi ya kamili, kanzu ya mkia, tai nyeupe, tai nyeupe na mikia, wamevaa vizuri mtu, suti, suruali nyayo, pantsuit, mtu wamevaa vizuri, and suti ya suruali. There might also be nyayo, suti ya nguo, seti, seti ya nguo, bridesmaid, msichana wa heshima, mjakazi wa heshima, slack suti, and suti slack.