If your father gave you his house outright (so that he longer lives in it, he doesn't benefit from it and there were no conditions placed upon you when the property was transferred) then if he lives for 7 years from the date of transfer the value of the property will not count towards his estate when it is assessed for (possible) Inheritance Tax purposes.
If your father gave you the house outright (as above) but he does not live for 7 years, then part of the value of the house (based upon a sliding scale) will be considered to be part of his estate for Inheritance Tax purposes.
If your father continues to live in the house (or otherwise retains an interest in it) the property transfer will be considered to be a 'gift with reservation' and the whole of the value of the house will always count towards his estate, for Inheritance Tax purposes, irrespective of how long he lives for. (The only exception would be if he's paying you the current market rent to live there).
It should be remembered that if the value of your father's estate (including the value of the house, or part of it, where relevant as above) comes to less than £325,000 then no Inheritance Tax is payable anyway.
http://www.hmrc.gov.u...-home-to-children.htm
Chris