Arm of the Atlantic between Great Britain and the N European mainland (5,3)

I believe the answer is:

north sea

(Other definitions for north sea that I've seen before include "'It lies between Britain and Scandinavia (5,3)'" , "large body of water" , "It's not land to our East" , "Water beside UK" , "British oil/gas area" .)

I've seen this clue in The Independent.

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