Old place name, rum as can be (5)

I believe the answer is:

sarum

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'old place name' is the definition.
The definition suggests a singular noun which matches the answer.

'rum as can be' is the wordplay.
'can be' indicates an anagram.
'rum'+'as'='rumas'
'rumas' is an anagram of 'SARUM'.

Can you help me to learn more?

(Other definitions for sarum that I've seen before include "Ancient name of Salisbury" , "Wiltshire diocese" .)

I've seen this clue in the Evening Standard.

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