Sholay's having a bad day!
1. Nobody is classified as an 'adult' by UK law until they're 18, not 16.
However . . .
2. There's no statutory law which states when a young person can leave home. (Sholay seems to have got confused with the law on marriage). In cases of family breakdown, some young people leave home to live (with the support of social services) in their own flats well before school-leaving age. (I've taught several 14 and 15 year olds who've left home).
In general, however, 16 is usually taken as the age when people can leave home. (For example, if a 16-year-old 'runs away' and the police find out where they're living, the parents have no right to be told the wherabouts of their child if the young person wants their location kept secret. The same would not normally be true for a young person under-16 years of age).
This link does not deal with the legal position regarding young people leaving home but it may still be of interest to you if your daughter may be about to leave home:
http://www.parentlineplus.org.uk/index.php?id=362
Chris