Outflow of British capital (6)

I believe the answer is:

thames

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'outflow of british capital' is the definition.
The definition suggests a singular noun which matches the answer.

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(Other definitions for thames that I've seen before include "The Isis at Oxford" , "Shipping forecast area" , "Longest river in England" , "The Ma's in the river" , "One going to live abroad" .)

I've seen this clue in The Globe and Mail.

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