This is one of a series of caches within the boundaries of Beckenham Place Park. You'll find more details about the series at this cache: GC9B550
You are looking for a very small magnetic metal pot.
As the pot seems a little leaky I have replaced the log with waterproof paper - biro or sharpie seems to work best on these. Also log may spring out at you when you open pot - you have been warned! 
Hidden with kind permission of Lewisham Council