I found this a while back which records the various lockdowns:-
www.instituteforgovernment.org.uk/sites/default/files/timeline-lockdown-web.pdf
The increase in numbers in Septembers was, if I remember correctly, linked to Students going to University and then passing it back to families as they decided to go back home. A bit of a red herring possibly that initially distracted from the Kent Variant.
During October Kent numbers grew (as mentioned earlier blamed on prisons) and crept into Essex and the East London Boroughs. Lack of social distancing and 'white-van-man travel corridors" were heavily blamed.
Lockdown in November saw numbers in many areas fall, but in Kent, Essex and East London numbers continued to rise. I remember commenting at the time that I couldn't understand how in lockdown the East London Boroughs were spiralling.
Some time in January, it was estimated that the boroughs of Newham, Barking, Havering and Redbridge possibly had infection rates as high as 1 in 3.
It will be interesting to see whether the arrival of the Indian variant results in an increase in vaccination uptake - it was certainly very busy when I had mine today and they turned away anyone without a booking.