My OH is working on a farm renovation for someone - I cannot believe the hassle they have from the council. Apparantly they had to stop work and apply for engineering work permission ....er ....engineering? As far as I could see they were digging a banking out at the bottom of the field. Then they tried to remove an old slurry tank from the ground .....oh stop!! Yes, they needed the engineering permission again Thats only two examples - there are plenty more!!.
Hopefully, you can do your pond - if the council get involved, they will be doing risk assessments etc. and demanding to know what you will do to stop kids getting in the pond etc.
It is a dilemma - if you do it and then they don't like it .....on the other hand, I would do it, and hopefully there will not be a problem. Anyway, a pond is an asset to the wildlife etc. surely?