Hello again jvf,
In British pounds, the amount you inherited is equivalent to approximately 4.4 million British pounds.
In the UK, any estate that is valued over 312,000 pounds is subject to inheritance tax. The current rate on that tax is 40% of the excess over 312,000 pounds, so in essence, there is going to be something close to the equivalent of $3 million US dollars due in inheritance tax payable to the UK.
If your relative had an executor for his estate, then the executor should have already filed the estate tax return and paid these taxes out of the estate. However, if there was no executor and you are the sole heir, then it sounds to me like you are the one who will need to take care of filing an estate tax return on behalf of your relative and paying the appropriate inheritance tax is due before they will release that money to you. Once the money is released and you bring it to the United States, no tax will be due in this country, but you will need to report receiving the money on Form 3520 as mentioned in my earlier post.
You are probably going to need the assistance of a tax consultant who can help you file the proper forms in the UK. I am giving you a link below to a company named Ocra who has offices worldwide and could more than likely help you with the filing of the necessary forms.