Yothean, unfortunately you are highly unlikely to gain any sort of scholarship for a masters courses (particularly for law). If you are to obtain funding, it is most likely to come from your own country.
Try 'directly' asking Essex for a list of scholarship providers, and visit the British Council website as they also have scholarships for international students.
The only scholarship that I can think may apply to you is Chevening :
http://www.britishembassy.gov.uk/servlet/Front?pagename=OpenMarket/Xcelerate/ShowPage&c=Page&cid=1065718181044
Try Googling: 'cambodia scholarships'