After an argument with my ex - who is paranoid he'll be getting a fine because it's his day with DS, I sent this email to the head:
I have told the office that will be absent tomorrow. When I put in my request, it was marked as unauthorised. As a head, I think you should understand the implications of that on our family.
We are going to a family birthday. He lives a long way away so it is impractical to leave after school. So I decided that we would get the early train and go to London to see the British Museum. I always try to encourage education when we are out.
Classifying it as unauthorised has caused a lot of stress and friction. is worried about getting a fine and TBH, so am I. It is his day with but I am taking him. He is worried and has asked me to copy him in so everyone is aware that he is not responsible.
I am responsible. So any fine should fall on me. I do understand why Gove has introduced this and the role of absences figures and OFSTED. I have worked in schools with 50% attendance. But we are not taking advantage of cheap term time holidays. We are just asking for a day off to attend an important family event.
We are supporters of the school and are very conscientious of and ensuring he takes school seriously. The alternative was to tell school he was sick. That would of course be encouraging lying and that is not what we do.
I really hope you understand the effect of this policy on families. Your decision has caused arguments and friction. Yet when I was teaching, we had children off for the Yorkshire show and that was authorised because it was a good thing to do.
*** will not be in school tomorrow. It would make our lives a lot less stressful if it was authorised but I understand if your hands are bound by bureaucracy.
Plucks at the heart strings 
But I do think Heads should be aware of the impact and stress this causes.