Anyone know about casting agencies for film and tv work ? (how to, college)

[BethfromEngland]

Hi.Does anyone have any advice on how to become an extra for film and tv work ?.I've been thinking of doing this for a while now.I'd like to start off as an extra for the time being.

I studied Performing Arts at college, and have been a member of a couple of local drama groups in the past.

Anyone know of any good, reputable agencies, preferably in England to start off with, although eventually i would like to work abroad.