I am not sure about resigning but I found that if you try and extend they seem to loose your papers at RHQ and then a lttle while later tell you your due out date is a month away and that unless you sign this form now you will be out of a job in a weeks time.
I believe you have to transfer to the reserve list. What ever that means.
There are pages of how to do it in AGAIs - it will tell you who you have to write to, what forms to fill in, when to get a medical, whether you can work during you resettlement or terminal leave. Speak to your Chief Clerk (or someone else's if you haven't told your CO yet). Be prepared for the 'Are you sure? There's a rosey future for you here?'. Then comes the 'I don't know whether we can let you go on that date' At least the number of whatchkeeper posts in NI has reduced - a favourite to mess people around for 6 months.
There is a new form for Officer resignations. Interesting bit is para 12. Apparently the Army is compiling PVR statistics to identify recurrent themes amongst leavers in order to inform policy making. And the reasons we give for getting out aid this process. There is a long list (Compassionate, emigration, firm offer of civvy job, general employment prospects as a civvy, live in ones own house, spouses job, sexism, racism, own pregnancy, medical reasons, pay & allowances, childrens education, standard of army accommodation, operational overstretch, lack of current job satisfaction, hatred of satff jobs rather than RD, Pension, seeking fresh challenges etc)
And you can expand in a text box. Then they ask you what is your main reason from the above.
And there is one final trick question. they ask what would encourage one to stay in. I could have lots of fun answering that question.