This is worth pursuing.
Ask them for the schedule of maintenance relating to that particular lamp post. You need to know when it was last inspected / repaired / maintained.
The question will then be - was this reasonable and has the Council fulfilled its duty of care?
If it hasn't been inspected or maintained for a lengthy period you could claim that the canopy came adrift in high winds due to the Council's negligence.
It is not good enough for the Council to claim there has been no reports of the canopy being loose. This is not like potholes which are easily seen by the public and the Council should not be relying on reports of poor maintenance for something that is so potentially dangerous and very difficult for the man in the street to spot.
Look at your own home insurance. Are you covered for this? If so, it may be worth claiming through them and letting the insurance company recover the monies from the Council.
Even better if you have legal expenses insurance - contact them for advice.
However, it will be inexpensive to pursue this through the small claims court - you can do it online.
Keep copies of all correspondence, and a written diary of any phone calls, letters sent and received, action taken and so on.