The primary consideration of the court will be in the best interests of the child. There are a number of factors that the court would take into account when determining this.
If a child is living in the UK then to remove that child from the UK requires:
If someone removes a child without either of these then they are potentially committing a criminal offence.
There is an exception to this where there is a child arrangements order in place. The person named in the child arrangements order who the child lives with is able to take the child out of the UK for 28 days.
If you cannot reach an agreement then you need to consider making an application to the court for a specific issue order.
Before doing this it is important to ensure that you have made real efforts to discuss the proposed move with your former partner and you have properly considered the concerns that they have raised. It is also crucial that you have reality tested the plans that you have made to ensure that they will work on a practical level. Mediation can assist you with this.
If you believe that there is a real risk that your former partner may take your child abroad without your consent then you may need to make an application to the court for a Prohibited Steps Order.
Depending upon the urgency you may also need to consider making an All Port Alert to prevent your child leaving the UK.
The primary consideration of the court will be in the best interests of the child. There are a number of factors that the court would take into account when determining this and these will be highly fact specific to your child and their best interests.