Hi --- You only need worry about inheritance tax if your Dad's total estate on death exceeds the current single persons IHT threshold of £312,000 pounds (rising yearly)
This estate figure will also take into account the value of any gifts he has made in the Seven years leading up to his death.(after Seven years they are not added to the estate, simply disregarded)
As it looks, your Dad's estate would not be liable for any IHT as the total value of his estate for tax purposes is £40k + the 3 gifts made total £75k equals = £115k total estate....... meaning his assets are well below the current £312k tax threshold.