Management won’t fix flooding from main drain in my ground floor flat!

Dear Mike,

I suggest you employ at your expense a contractor to undertake a video survey of the drain. This should extend from your flat along and communal drain until it reaches the drain for the street. The contractor normal produce a map of their findings along with a copy of the video footage and a description of the type of blockage.
Depending where any blockage is situated could determine liability for the clearance/repair. The responsibilities of water companies has changed and they have a more extensive liability which depends on the layout of the drainage system.
Yes you could be out of pocket but better that then uninsured because of a known defect.

https://www.amazon.co.uk/Flexible-Professional-Drainage-Cleaning-Unblocker/dp/B0CK98QQRP/ref=asc_df_B0CK98QQRP/?tag=googshopuk-21&linkCode=df0&hvadid=676270497790&hvpos=&hvnetw=g&hvrand=13715390876911984053&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=1006663&hvtargid=pla-2268822195314&psc=1&mcid=0d1d0cd76368318bb5757ae7b04eb38e&gad_source=1
Now this is a drain rod set on amazon. You could buy this and try to clear the drains yourself
Might save alot of hassle

You contribute to maintenance costs through your service charge. You have legal statutory right to inspect survey report under s21 landlord & tenant act and so serve on man co/landlord notice (template off internet).
Next time take photos of flooding, times,dates, weather alerts.
It suggests drains cannot cope due climate change and is a major repair funded out of
Reserve fund or man co block insurance.
If you suffer damage to your own contents then claim
on your own contents insurance policy and pursue man co on that basis.