If you father resides in Great Britain and is in no shape to knowingly sign a new power of attorney, your best option is to consult with an attorney experienced with powers of attorney and the requirement for them to be valid in the state where your father's real property is located in this country. Potentially the British power of attorney may comply with the requirements for a valid power of attorney allowing you to sell the parcel that you have inquired about.If not, and you need to sell the property in the United States, most likely you will need to have a conservatorship established as to your father's assets and himself as well. Given the fact that he is residing outside this country, the proceeding which is expensive and time consuming will have to be done in Great Britain.Good luck.