After a divorce or separation, the parent taking care of the children may wish to move to another area or country.
If the move involves relocating outside the UK, then permission must be obtained from the other parent, otherwise the removal could be classed as the criminal offence of child abduction which is a serious offence that usually results in a custodial sentence being imposed.
It may be possible for both parents to agree to the move in which case you may wish to consider having an agreement drawn up and signed by both parties. To avoid any future problems, you may also wish to have a consent order drawn up and submitted to the court. Once granted, the agreement becomes legally binding.
If an agreement cannot be reached, then an application will need to be made to the court who will consider the reason for the planned relocation and what arrangements can be made for the children to have contact with the other parent.