The only benefit which your son's National Insurance contributions will have covered is Incapacity Benefit. Details here:
http://www.jobcentreplus.gov.uk/cms.asp?Page=/Home/Custo mers/WorkingAgeBenefits/492
There are two other benefits which your son might be able to claim. These are Council Tax Benefit:
http://www.dwp.gov.uk/lifeevent/benefits/council_tax_ben efit.asp
and Income Support:
http://www.jobcentreplus.gov.uk/cms.asp?Page=/Home/Custo mers/WorkingAgeBenefits/493
The goldenrule with all benefits is "If in doubt, claim!". (As long as you answer all questions honestly it can never do any harm to try for a benefit).
Althogh I hope that I've listed the principal benefits available, please ensure that your son contacts his local Citizens Advice Bureau. Their staff are all trained in dealing with problems like those of your son.
Chris