I live in Ontario Canada my children were born here but my wife and I are English.
Last year we decided to separate for a short while and she went back to the U.K. with the children . I wrote a letter giving permission for them to travel for a period for a vacation only ( not Perm) . Now my wife has decide that she wants us to split for good and has already having a relationship with another man.
My question , how easy or possible would it be for me to get the children back over here to Canada seeing as I have never given permission for them to live there in the U.K. perm.
Also the mother is being rather unfit, partying every weekend and palming the kids off onto her parents.

I understand your anger. Do you truly believe she is unfit? Or are you just hurt angry and jealous? Be honest. I think you will find in Britain they tend to side with the mother. Are the children happy in england

No please don't get me wrong . I am not at all angey , well just a little obviously but sad more than anything. The children do have a bigger family network over there, but there emother is going out partying all the time and is now spending a lot of time with her new man and the children ar egetting palmed off onto her parents that are getting older and have never had the patience to deal with young ones , which is understandable. My concern also is whether they ar ebetter off there or here and if she had her own place and was being a good mother I would not be thinking this route. But when I call to speak to the children the day after she has been out and they say mummy is in bed at 2 in the afternoon I know that they are being neglected. And the only place she takes them out to is the local football club so she can drink and they run around for an hour.

I think it should come down to what's best for the children. Their mother sounds immature, but it doesn't make her a bad mother by any means. She is also dealing with the breakup of your marriage, new man or no new man. It must effect her. Try to stay talking to her.
Personally I think Canada would prob be a better standard of living for the children, and I feel that when they are older you will prob find they come to visit you a lot or even move in with you.
I think court cases can be messy and disrupive for children.
Best advice, stay calm, remain friendly with ex wife for kids sake. Go to england on holiday, suss out how happy the kids are, talk to them. Then proceed. If you feel they want and are better off with you then, fight for custody.

If she seems to prefer partying to caring for children, she shouldn't be opposed to having you take care of them full time. If she's sleeping till two in the afternoon, partying is the winner. The above advise is good, now. If she has alcoholic tendencies and it's easier to drink in England, she'll want to stay.

If it were me, I'd go and get them. Make her jump through hoops to get them back.