Separation period

I would like to have clarity on count of separation period of one year.

When does it start?
From the day you start leaving separate or from the day you prepare separation agreement?

Eg. I have been leaving separate from my partner since march 2015 but I have not done any process of separation like separation agreement etc.

Will my separation of one year be considered from March 2015 or from the date I process separation agreement?

Thank you

You are legally separated as soon as you begin living under different roofs, with the intent to remain separated. Whether or not you have a separation agreement in place is inconsequential. If you have been living apart since March 2015 then you have been legally separated since then.