Hi, sorry I was offline when you replied. You neither resigned, nor were you dismissed from this job - leaving under a settlement agreement is basically a mutually agreed exit, so you do not have to say you resigned. As to the reasons why you left then you can go into as much or as little detail as you wish - if the reference is basic then it will not really reveal any details about the reasons for leaving so you do not have to say more than you want to, you can be as economic with the circumstances as you wish, obviously without lying.
Hope this clarifies your position? If you could please let me know that would be great, thank you
Please let me know if this has answered your original question or if you need me to clarify anything else for you in relation to this? Thanks