oooh interesting
first of all you would establish under the MCA whether of not the YP has capacity to make the decision about leaving the ward in a variety of circumstances. e.g do they understand that they may leave for short periods of time but must return, or do they just want to leave and just don't understand that this may be detrimental to their health? (the case study won't necessarily tell you this but these are questions you could pose in your essay). Does their capacity fluctuate - for example if they have been drinking. You would be looking at best practice in that respect of ensuring that you had given them every possible opportunity to make a a capacious decision.
A person would meet the first criteria of requiring a mental capacity assessment under the MCA as they have 'a disturbance of the brain or mind'.
If a person has capacity to understand their choices/ make risks then they cannot be detained against their will under the MCA but they could still be detained under the MHA if it is felt that they have a mental illness.
If a person lacks capacity then a best interests meeting must be held (guidance again in the MCA) to determine what the best course of action would be to keep the person safe, in line with any previous wishes. Views of family and friends would ordinarily be sought but in this situation where the YP is not 'befriended' then an Independent Mental Capacity Advocate (IMCA) would be commissioned.
If the BIA is that the person should remain on the ward then the DOLs application gives the legal go ahead as it were for the doors to be locked to the ward so that the person cannot get out, or for other restrictions to be put in place for example a care worker distracting them from wanting to leave.
The government guidance is pretty good on this subject (<a class="break-all" href="//lwww.justice.gov.uk/downloads/protecting-the-vulnerable/mca/mca-code-practice-0509.pdf" rel="nofollow" target="_blank">ink to the MCA guidance here)
I've given you a pretty brief summary of the basics there - you may know all of this already! If thats the case and you were needing something a bit more in depth let me know.
Is it a Social Work degree you are doing or something else?