Hello Juien,
I live in the UK and it used to be very strict here, more than any other country. However since the 1 January 2012, the laws have changed to meet european standards and agreements have been made to other countries from round the world. If you look up DEFRA, basically if you have a pet passport and all necessary vaccines, taking most pets ie dogs and cats to Sri Lanka is straight forward. So should you want to bring them back, as long as they are chipped and kept vaccines upto date is pretty easy. I think its just a small admin fee to pay at the airport which I think is between 500-1000 lkr. The srilankan embassy in london or a air transport company have more info on this.
I am myself considering bringing my 2 dogs, so they can can enjoy the beach and good weather with me.
Let me know how it all goes.
roderick