Is it illegal to let a house and sublet all the rooms? even tough i dont live there?

i rented this house for my family but by the end of the third month they went away leaving me with this huge responsability of 1500pcm then a started to rent the rooms. two months later i saw a little proffit. i charge 55 pounds per person and there is no more than two people in a room. all bills included even sky tv and internet.but i am not living there anymore. every sunday i go there to collect the rent and check if the house is ok, i believe that i am taking care of the house better than my landlord. i am afraid that i am doing somethin illegal, (not mentioning that i am a foreing person from the EU, so i will be liable as the same as UK) is it a crime? the profitt doesnt worth that.