Clue - The planned armament was two 20 mm cannon and two .50 in machine guns.

Blackburn B-48 Firecrest ?

Not built in the UK ???

Grumman XP-50.

Well done Jim it is the XP-50.

LINK - http://en.wikipedia.org/wiki/Grumman_XP-50
And the prize of course.

This weeks headache.

Have fun

Curtiss HS-1 (1917)

It looked like a Curtiss to me and searched for: early pusher Curtiss flying boat...

WOW, very quick & well done, it is indeed.
An interesting aircraft.`Two HS-1Ls operating from Chatham, Massachusetts made the only confirmed aircraft attack on a German U-boat in American waters on July 21, 1918, but this was unsuccessful, with bombs failing to explode and the submarine escaping`
LINK- http://en.wikipedia.org/wiki/Curtiss_HS
And of course the coveted prize.

Yes, well done!

This weeks headache??????

Have fun.