Another theory for the less aggressive nature of British forces by 1944 is the "special forces paradox."
Since 1940, so many volunteers had been called for, to serve in various specialist units, that the regular line units had been, to an extent, stripped of their more aggressive troops.
Just to quote the units I can think of at the moment, there were the Commandos, the Parachute Regiment, the SAS, the SBS, the Chindits, the Small Scale Raiding Parties, the Long Range Desert Group, the Special Operations Executive, Popski's Private Army... not to mention the more general "volunteers for hazardous duty" within all the arms of service.
All of these units achieved results out of proportion to their size- but it is arguable that the loss of those soldiers with the most initiative and drive damaged the effectiveness of their "donor" units.
It is not that the regular line forces lacked courage- far from it. The loss shows more as a loss of flexibility, both in responding to setbacks, and siezing opportunities when they were presented.