If your friend's insurance company will insure you with your UK license and does not require you to obtain a state, Florida, license then you should be fine to drive with it. Most insurance companies though require that a foreign license be replaced by a State license from the state in which you are residing.

If you are visiting Florida for a short time, a year or under you may use a driver’s license issued by another state or country. However, if you choose to stay in Florida for more than a one year period or accept employment within the state, you will have to surrender your UK license and obtain an official Florida drivers license.

For more information on Florida statutes regarding foreign or international licensed drivers check with the FL HSMV. Your friend should also check with his or her insurance carrier to make certain you will be covered with your UK licence and will not be required to acquire a Florida license to be properly covered by them.