Inheritance Tax (IHT) isn't paid on property, per se. It's paid on the total value of the estate.
So, if the £120,000 house makes up all (or most) of the deceased person's estate, there will be no IHT to pay.
However if the deceased person also had £380,000 in the bank (or in shares, etc), the total value of the estate would be £500,000. The first £325,000 would be exempt from tax. The remaining £175,000 would be taxed at 40%. (i.e. IHT due = £70,000).
More here:
http://www.hmrc.gov.u...eritancetax/index.htm
Chris