RACS Umbrella Group- HELP

I've just started with an agency and was asked of three options if I would like to be paid via BACS umbrella group- could anyone enlighten me as to what it is exactly and how it is beneficial and the charges that apply. I asked the agency lady and she said she couldn't give me more info as didn't know much about it, but did say there was obviously a reason so many locum dnetla nurses use them.

Any help would be gratefully appreciated.