Worth a try, they take frozen food and they collect within the M25
https://cityharvest.org.uk/food/#:~:text=Once you've identified the,(ambient%2C chilled or frozen)
https://fareshare.org.uk/giving-food/the-food-we-take/
If you input SE15 into the search on this website it brings up a local pantry that takes frozen food
https://www.yourlocalpantry.co.uk/help-a-pantry/donate-food/