Amazing shoot which swept across the whole of London (5,4)

I believe the answer is:

great fire

I'm a little stuck... Click here to teach me more about this clue!

'swept across the whole of london' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'amazing shoot' is the wordplay.
'amazing' becomes 'great' (I can't justify this - if you can you should believe this answer much more).
'shoot' becomes 'fire' (as in firing a gun).
'great'+'fire'='GREAT FIRE'

'which' acts as a link.

Can you help me to learn more?

I've seen this clue in The Irish Times.

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