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.
Free Auto Insurance Quotes
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.
Comment Update:
We'd love to know what you think about our comparison tools. With your feedback (both good and bad!) we can further improve our tools for the future and smooth out any difficulties you may have had.
Call us on:
0870 112 8239
(Mon-Fri: 10am-6pm)
[Let CarInsurance.com help you find affordable auto insurance now.] In addition, read this news article on purchasing Insurance for a Short Period of Time. | 
