Originally Posted by Manitoba
Most countries have laws about enforcing foreign child care obligations. Not sure of the procedure for the UK but I did read about it being in effect in Canada a few years ago. As I recall the custodial parent had the option of having the foreign ruling enforced or a new amount calculated under Canadian rules. The Canadian courts would not even look at overturning a custodial order of a foreign court.
The OP should get good legal advice and not take the word of random internet strangers.
The problem is "service of notice."