What appearance does the British stars in American films have upon the British films?

Many British stars have found success in Hollywood films. For example; Robert Patterson in 'The Twilight' saga, Keira Knightly in 'Pirates of the Carribean' saga, Vinnie Jones in 'Euro Trip', and Ewan McGregor in 'Moulin Rouge!'. This promotes the actresses and actors, but it also means the stars lose their roots and become just another part of Hollywoods 'showcase of stars'. However, in the last five years Keira Knightly has appeared in 'Pride and Prejudice' and 'Atonement', both successful British films.
Kate Winslet, who has also become a big Hollywood actress, visits back to the UK regularly to appear in films and TV shows. She is an example one British/Hollywood actress who has kept in touch with her roots.
Many American films are well promoted, (as the Hollywood industry have a large enough budget to pay for it) which means that the stars are well promoted. People begin to recognise the names of stars, and their names stick. Also, if people like a British star in a Hollywood film, the chances are they will want to see some of the British films they started off doing. Giving them a wider fanbase, like Robert Patterson for example. American filmmakers taking British talent could be seen as a compliment to the UK, as it is showcasing the UK's talent in huge films. Some great actors.actresses in the UK wouldn't get the chance to be successful over here, but Hollywood filmmakers have the power to make them big. When British stars appear in Hollywood movies , filmmakers demand them to reprise their roles in sequals if the first film is successful.
The impact of British stars appearing in American films is that it gives the stars a chance to show their talent to a new audience. Unfortunately this can often drive them away from their roots.

This can also work vice versa - American stars in British films can attract an American audience to the British film industry, giving it a wider fanbase. For example, Guy Ritchie got Brad Pitt to appear in the British film Snatch. This meant that a wider range of audiences would watch the film, as the Americans would watch it for Brad Pitt, and the British people would watch it because it is a British film.