In blood vessel, new poison (5)

I believe the answer is:

venin

'poison' is the definition.
(substance in venom)

'in blood vessel new' is the wordplay.
'in' means one lot of letters goes inside another.
'blood vessel' becomes 'vein' (vein is a kind of blood vessel).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'vein' enclosing 'n' is 'VENIN'.

(Another definition for venin that I've seen is " Poison".)

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

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