Terrible solar performance in London since September 2024

I've noticed a significant drop in my solar panel performance since September 2024. On average, I'm seeing a 30% to 50% reduction compared to what was predicted. The installation seems to be working well, and it was spot on with predictions between June-August 2024 (even producing a bit more than expected). Is this drop due to the UK weather, or could there be something wrong with my panels?

For January 2025 for instance it was predicted I would produce on average 198kWh but only produced 126kWh.

Is there a website that provides monthly statistics I can use to understand if on average some months have been particularly bad/good in terms of average sun energy received during the day per city?