I would like to know if it is necessary for a back to work interview if your off work with a painful migraine now and then when the work knew you suffered with them at the time of taking you on in their employment.

Necessary, no but they can require one if they want one.
How long have you been off work

What type of leave were you on.

If they knew you had them, but if it is still effecting your work, and ability to do your work, they do not have to keep you if you can not do your work or if you miss too many days