What if: Operation Sealion, summary of an exercise held in 1974.

  That could actually be a good thing.  The forces that enabled Compass is likely to be assembled later but possibly if their engaging in the historical campaign in Cyrenaica when the Greeks ask for British aid, or simply General Metaxas doesn't die as OTL.  [He seems to have realised that inviting in British forces would prompt German intervention so he opposed it]. 

 As such a slightly later Compass, although possibly not much later given how decisive the defeat of the invasion of Britain has been, could avoid British intervention in Greece.  This would mean that Hitler probably has to decide whether to aid the Italians in Libya or Greece and probably deciding on the latter.  As such if Britain is able to rebuild its forces in Libya, with additional reinforcements and advance on Tripoli while Hitler is attacking Russia you could see the N African campaign ending a couple of years earlier than OTL.  Which would have huge advanages for Britain.  [One of my favourite PODs is some varient of this.  You can get massive butterflies, both in Europe and the Far East.]