I can sell one to you Scarlett, but it will have to be in the format "Field Marshall Scarlett (University of Thornton Heath)". I'll do you a PhD for a mere fiver extra :)
Given what others have got away with in the matter of a name-change by deed poll, I'm sure you could call yourself 'Field Marshal Lord Scarlett' or whatever. However, that would just be your name, not a title. To have the latter you would need to be a member of the peerage and have acquired high rank in service with the Army. Go for it!