Got an ex-brother in law who left the army after about 7 years, he spent all his resettlement on a plumbing course and now sells ladies fashion on ebay. I think the army career advisers are caught up in the fictional belief that plumbing = profit. This all started about 7 years ago when a national paper reported on some 50k a year bankers who retrained as plumbers so they could have more money and less stress than being bankers.
Since then the industry has become over subscribed with fast trackers and the likes under-cutting prices almost to the point of melt-down.
If I could have the last 10 years back, I'd not be choosing plumbing as a career path.
Plastering yes, painting and decorating yes, domestic electrician yes, plumbing no. Most plumbers will tell you that they are working silly hours for comparatively little gain in the current climate. Things like speedfit and certain TV programs/youtube vids are making this profession look so easy that customers aren't willing to pay what it's worth.
I would recommend that you have a re-think about your career path to be honest. Being a self employed plumber can be good, but the truth is that it probably won't be.