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Not so long ago, Britain was held in such low esteem in Iran that it was simply dismissed as the "little Satan". So far as the ayatollahs were concerned, the real enemy was America, the "great Satan", whose love of liberty and free market capitalism was thought to pose the gravest threat to the Islamic revolution's survival.

It was for this reason that the American embassy, rather than the British, was occupied by the Revolutionary Guards in Tehran soon after Ayatollah Khomeini seized power in 1979, and its 66 staff held hostage. The expansive grounds of Britain's diplomatic mission, which hosted Winston Churchill during the Tehran conference in 1943, were briefly occupied by the Guards during Iran's revolutionary turmoil, but then evacuated because the mullahs did...