The concept of boost Cut out is similar to WEP but different
Here is a simplifed description of how it works.
Most RAF/Luftwaffe aircraft had Boost controllers (Most US aircraft at this stage didn't). With Boost control engaged (the norm) the pilot selects the required Boost then as he climbs or descends the Boost controller holds the selected Boost constant without any further pilot action required (below Full throttle height FTH)
In a no Boost controller aeroplane the throttle would need to be progressively opened as you climb until you get to Full throttle height (FTH).
The second function of the boost controller is to limit or "Boost protect" the engine to a rated limit. So the pilot can select Full throttle knowing he is not going to "overboost" the engine. If not equipped with a Boost controller then the additional pilot workload is required to ensure that Boost limits are not excedded.
Boost cutout simply resets the Boost controller limit to some other value above normal rated Boost. In the case of the Spitfires Rated Boost for the MKI, 1A was +6.25Lbs, with MKII at +9lbs. In all cases once Boost Cutout is selected (in the case of the Spits pushing the red boost cut out lever forward and selecting full throttle) will give you +12Lbs boost up to the respective FTH (about from memory 10,500Feet). If desired the pilot could then rotate the Boost cut out switch back (cant do this at the moment in COD on the Spit .. it should be a toggle control). Once done the Boost controller is back using its normal +6.25/+9Lb limit. In the case of the Hurricane the Boost Cut out was a plunger arrangement which works correctly as a toggle in COD. However no change in Boost is evident on the boost gauge.
Its also worth pointing out that at the time of BOB most Boost gauges didn't go up to +12Lbs so Boost cut out (Below FTH) would result in Full scale Boost deflection.
Running at +12lbs brings with it additional cooling and engine wear problems.
As others have stated +12Lbs Boost was only possible if 100 Octane fuel was being used. Its fair enough to state that all operational RAF fighters were running 100 octane fuel during the battle.
So this area needs to be tweaked.