> I have already booked train ticket so think im too late to break up the journey
It depends on what kind of tickets you have booked, and the train company as well... I know there are some which limit you to That Train at That Time Only, and if you missed it or had to get off at an intermediate station, you'd be expected to pay an excess or a new fare.
When travelling with my dog I've not booked ahead, mainly because I don't have a debit/credit card to do so, but a ticket bought on the day or on the train does give you more flexibility and occasionally I have had to alight at a station along the way and wait for the next one.
If you don't leave the station it's not counted as breaking the journey; however with a dog, you can sometimes sweet-talk the platform inspectors into letting you go out the front of the station for a few minutes if you say your dog needs to relieve itself! After all neither they, nor you, nor any fellow travellers want to see a yellow river of pee snaking across the platform... or even worse a highly public dump!
On a few occasions I have had to break the journey for welfare issues - one notable time was when my expected train arrived packed with people standing like sardines and crammed into every crevice because a whole carriage had been closed due to an exploding toilet. It was a very hot day, neither me nor my dog were happy with that, so I got off at the next stop 10 mins down the line... where we enjoyed a relaxed and comfortable hour's wait and picnic in a grassy park adjoining the station before getting the next train on. It's always worth seeing if these options are available to you when travelling with animals.