I would not advise it.

http://www.alamo.co.uk/helpfulinformation/us

"Prices given on this website are not applicable to residents of the USA or Canada or holders of USA or Canadian driving licenses. By making a reservation on this site you confirm that you reside outside the USA or Canada and are not a holder of a USA or Canadian driving license and accept that your reservation may be rejected at the time of pick-up if a USA or Canadian driving license is presented."


However if you did online check in fully and just need to proceed to the car, you stand a good chance of suceeding, with only the booth person you would need to pass.