John Green, you're not correct here.
Most UK/Irish arlines are as follows:
CP - 4
FO - either 2 or 3
Nobody wears 1 stripe that I can think of.
Whether the FO wears 2 or 3 depends usually of whether they have a full ATPL (3 stripes) or not and/or on length of service in company.
Some companies call pre-ATPL FO's SO's, but thats a pay distinction. And some call pre-ATPL guys FO's and post-ATPL SFO's.
So it depends on the company who is called what. But the bottom line is the guy in LHS wears 4 and the guy in the RHS wears 2 or 3 and nobody wears 1.