Careful. You have to give it, not leave it. You must do some research on gift tax, or the recipient may have to pay tax of up to 40 percent of the value of the gift. You can't make the recipient pay rent , either, or this becomes a "gift with reservations", which the Inland Revenue says is not a gift at all.
Start by going to the Citizens Advice Bureau, then, if they recommend, as they probably will, see a solicitor.
If a gift was given more than seven years before the giver's death, it should be free of inheritance tax, but remember, it is very difficult to evade tax without the services of expensive tax-experts and lawyers