Tricky one! Only because I fly out of Gatwick and not LHR. I am going to make an assumption here that there are no obstacles which limit the track to 3000ft amsl. In this case I would follow the MAP but tell the ATCO I was doing it so that if he forgot to mention that he wanted me to climb straight ahead, it might jog his memory.
Now, what's the correct solution?
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Very funny, Scotty. Now beam up my clothes!