Army recruiters indeed focus their efforts on C2DE youths in northern cities:

https://www.theguardian.com/uk-news/2017/jul/09/british-army-is-targeting-working-class-young-people-report-shows

http://www.independent.co.uk/news/british-army-targets-young-working-class-recruitment-military-marketing-drive-campaign-uk-a7833086.html

https://www.commonspace.scot/articles/11324/reports-find-british-military-targeting-working-class-recruits-and-creating-violent#

I suppose their strategy makes sense, though; would Cambridge economics graduates want to be shot at when they can earn million pound bonuses in the City of London?

The Samaritans' report on class and suicide can be accessed here:

http://www.samaritans.org/sites/default/files/kcfinder/files/Socioeconomic%20disadvantage%20and%20suicidal%20behaviour%20-%20full%20report.pdf

It shows beyond question that the groups most susceptible to suicide are defined by low socio-economic status (in fact, older working class men are the group most likely to kill themselves - doctors are outliers).