I do not think that the UK could have defeated Germany alone -- without Russia siphoning off German troops, without the assistance of the Commonwealth, without the assistance of the US.

The UK lost all or almost all of its heavy equipment and most of its small arms at Dunkirk (not to mention the troops). The Hurricane and Spitfire were superior, overall, to the ME-109 and the Focke-Wulf, but production wasn't as fast as it should have been -- the Battle of Britain was a damned close thing!

The Germans had radar (albeit nowhere near as good a Britain's), and ASDICS was a multi-national developement:

Asdic was a term used to describe echo location and ranging using high frequency sound waves. It grew out of experiments undertaken by French scientists in the early 1900s on the propagation of sound in water. Of particular note is the Fessenden electromagnetic oscillator which was a precursor to the modern transducers used in sonar, the term now applied to Asdic operations. Other French scientists contributing greatly to the work were Langevin and Chilowsky who developed techniques for transmitting and detecting the sound waves. In 1915, NZ scientist Ernest Rutherford and scientists from the British Bureau of Investigation and Research (BIR) developed the process further and the first Asdics were ordered by the Royal Navy in June 1918. In the USA, experiments continued at Columbia University which lead to the formation of research teams combining the US Navy, the Submarine Signal Company, General Electric and Western Electric at Nahant, MA. Asdic research stepped up at the start of WW1 but it was not ready by the end of the war, and didn't get to sea until 1920, when one was evaluated on the cruiser HMS ANTRIM. Four patrol vessels were also fitted with Asdic on an experimental basis, leading to adoption of a production Asdic system in July 1922. British submarines were fitted with Asdic beginning in 1926. It was in service in British destroyers from 1928.

WW2 was won by team effort, against the Germans, the Italians, and the Japanese. I don't think one country along could have done it.