We are sub-renting from the 23/12 to the 01/01 our double bedroom in a 2 bedrooms flat located in Liverpool Street. The other bedroom (roommate) will de empty from the 24/12 to the 31/12 so you will mostly have the flat for yourself.
About the rules, nothing very special. The cat will be living with you during your time (you don't have to taking care of her, we'll be paying someone to do it, though she loves hugs). You can not smoke in the flat but we have a balcony and you can go there. And just basically, be respectful with the place and our stuff, that's all :-)