After months of revelations by Edward Snowden about the extent of global surveillance by western security services, it has come as a shock to those pondering the fate of the missing Malaysian airliner that the extensive network of spy satellites in orbit have failed to locate the jet.

After a week of fruitless searching by more than 100 ships and aircraft, the challenge is becoming more daunting as the hunt switches to an ever larger part of the globe.

Expectations that the answer to the mystery would come from space were raised last week, when it emerged that data from commercial communications satellites, operated by London-based Inmarsat, had provided clues after military radar lost track of the Boeing 777 as it headed west over the Indian Ocean.