The UK and Australia are both signatories to the Hague Convention. The ex-wife would have to return the children to Australia - their habitual residence.

However, there is a strict time limit on Hague Convention child custody dispute cases ie. the longer the children are in the UK then it could be argued that the UK should be regarded as the children's habitual residence. The O/P would need to take action immediately if the children don't return on the originally booked flight back to Australia (there could be delaying tactics/excuses as to why they are staying on in the UK, to the disadvantage of the O/P).

Hopefully it will never come to such a situation, but it is best to do a little research and find out how to deal with such scenarios:

See here - including the comments at the end of the report:

http://www.marilynstowe.co.uk/2012/0...nifer-hollyer/

http://www.ag.gov.au/FamiliesAndMarr...abduction.aspx

There is a (UK based) charity called 'Reunite' which deals with international child abduction. Their website explains about the Hague Convention, lists of lawyers in the UK, Australia, USA etc.

http://www.reunite.org

http://www.reunite.org/pages/parenta...tion_faq_s.asp

http://www.reunite.org/usefullinks.a...ks_submit=Find

http://www.reunite.org/lawyers.asp?l...al_submit=Find

It might be worth checking with an Australian lawyer if you should have a letter drawn up, listing the names, d.o.b, passport numbers etc. of the children (and their mother) their flight reservation details of the flight to the UK and flight back to Australia and giving your permission that they are allowed to travel to the UK on the understanding that they are expected back in Australia on that day (the flight arrives back in Oz) - and to get it notarized/witnessed.


All the best