A thousand were banished in the month despot lost the head - right there and then (9)

I believe the answer is:

onthespot

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'a thousand were banished in the month despot lost the head' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'right there and then' is the wordplay.
'right' becomes 'on the right' (synonyms).
'there and then' becomes 'spot' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'onthe'+'spot'='ONTHESPOT'

Can you help me to learn more?

(Another definition for onthespot that I've seen is " immediately".)

I've seen this clue in The Irish Times.

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