This article from todays Times (29th May) will hopefully help prompt some changes.
A couple of years ago I visited a family in Speke. Without going into huge details, a 17 year old girl was happily there as a foster child, but the funding was about to end. She was applying for University courses and the family would have been more than happy for her to stay while studying at one of the Liverpool Universities or another one reasonably near. Yet because of the money situation it looked as if either she was going to have to put this off for a while or move out, with all the implications of that. She had had a difficult few years beforehand and by the sounds of things had turned her life around. The law, and with it the funding, needs to be changed to acknowledge that leaving the care system, or the support at the end of the care system, should be a gradual process which may well run up until someone is 21.