It isn't illegal until someone challenges it, he doesn't bother.
Errr Yes it is.
You obviously have absolutely not even the basic grasp of how the law works.
So if I steal something, that isn't illegal unless I get caught. ?
If I murdered someone it isn't against the law if I'm not apprehended ?
'Against the law' means there is a law written down and approved by parliament. It's a rule you must not break. If you do anything 'against' it. - that is 'against the law' and you will be punished - if you are caught. If you are not caught, it doesn't make it not illegal.
The law in this case is The Child Abduction Act 1984. The relevant law is this ;
The Act makes it a criminal offence for anyone “connected with” a child under the age of 16 to “take or send” that child out of the UK without the appropriate consent. “Connected with” includes parents, guardians or a person with a residence order or custody of the child. “Appropriate consent” is the consent of the mother, the father (if he has parental responsibility), the guardian or anyone with a residence order, parental responsibility or the leave (permission) of the court.
I know you wouldn't dream of it OP, but it appears some posters don't have the first idea - in fact think it's a good idea to post advice that could end you up in prison !
Hope it all goes smoothly and you get your new start.
If he does attempt to prevent it - you can self represent very easily. My advice would be to focus entirely on the additional support to raise your child that you will have in the new country. Do not start on about 'lifestyle' the court is interested in the child having an effective relationship with both parents (I know, I know) not if S/he will be able to ride unicorns twice a week because its so cheap.... so on that basis look willing. Offer twice weekly skype calls so child can start to develop a relationship. Offer for him to come and see her supervised every 8 weeks. If he has just decided to be awkward , he will soon stop any attempt at forming a relationship and stop at the Skype calls. If he is genuine and making a second go at being a father then it's only to your child's advantage. Skype can be the best way for that to happen -slowly. ( but we both know he won't be arsed - so all academic really)