Help! Can I move?

[Tonka76]

Advice please!
My partner and myself are buying a house 130 miles away from the city we currently live in with two children. My ex partner (father of DS who is 5) has had his solicitor send me a letter threatening a prohibitive steps court order. I have seen various threads with regards to this and I am not worried that he will win his case. We are able to buy where we are going and will therefore be able to offer the two DS stability and a more affordable life for us all. EX partner refused to leave the home when we separated so I was forced to move out with the DC. We will be moving near my brother with young children and will also be nearer to my older DS's father.
So my question is this... we are about to exchange and complete within 3 weeks. Can I still move while this all goes through the court? I completely understand that having your son move miles away is harrowing but I will make sure he stills sees him every other weekend as he does now and time in the holidays also. It is not my intention to take his child away but living in London is not an affordable option and I do not want to live precariously when we could have a secure home of our own.
I am seeking legal advice but there is a time issue here and I am not sure how to proceed right now. I would be grateful for any advice or thoughts. I hope I have explained things clearly!