Hi zahnartz62,
With the default key settings, pressing and holding the 'B' key will give you full brakes in British planes. Releasing the 'B' key will give you brakes off.
Differential toe braking was not used in British planes in WWII.
In order to brake with either the left wheel or right wheel you must tap (or hold the key if speed low enough) the 'B' key whilst applying left or right rudder to steer in the appropriate direction.
Alternatively you can set up key bindings for left brake and right brake.
In the cockpit the brake lever is the 'bar' that runs at a slight angle from vertical across the 'hoop' of the spade grip; but how it is used in the clickable cockpit scenario I'm afraid I do not know.
~S~