If you are visiting Great Britain as a United States citizen it is likely your U.S. insurance is not valid so you are correct that you will need to purchase insurance in England. Since you need the auto insurance for only a fortnight, or 14 days, I will presume that you are renting a car.

When renting a car in the UK, generally the rental agent will be able to sell you collision damage waiver (CDW). You might consider also purchasing additional liability insurance from the rental company. Most car rental companies will accept your US driver's license, provided that you are at least 23 years old and have had your license for more than a year.

If you need insurance above what a rental agency can offer you or you are looking to insure a car that is not a rental we offer car insurance in the United Kingdom. There is a link to their site next to the British flag on our car insurance home page.

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In addition, read this news article on purchasing Insurance for a Short Period of Time.