Four quarts of fluid in large oil lamp (8,6)

I believe the answer is:

imperial gallon

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'four quarts of' is the definition.
The definition suggests a singular noun which matches the answer.

'fluid in large oil lamp' is the wordplay.
'fluid' is an anagram indicator.
'in'+'large'+'oil'+'lamp'='inlargeoillamp'
'inlargeoillamp' anagrammed gives 'IMPERIAL GALLON'.

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(Another definition for imperial gallon that I've seen is " 4.55 litres".)

I've seen this clue in The Times and The Sunday Times.

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