I looked what being Queen's Messenger like the father is and I don't see why the family was so well off. They had a nanny, a Rolls Royce, and a very nice flat. This is what Wikipedia says:
"The Corps of Queen's Messengers are couriers employed by the British Foreign and Commonwealth Office. They hand-carry secret and important documents to British embassies and consulates around the world."share
They probably came from the British upper classes;
Earth. Welcome.
I think he was a spy or someone used to help the British spy network. The quote you have "they hand-carry secret and important documents to British embassies..." means he's be smuggling top secret messages and other things for the government. He was in Beirut when most of the action in the film took place.
sharePerhaps he married into the money. Nanny was the sister's nanny when they were children.
shareinherited money.
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