I assume its the boating lake ? there are in fact 3 lakes there.
The boating lake is unknown whether there is anything in there ,due to possible stealing of fish there. The ornimental lake next door (this is the bigger lake) is very narrow in plaes and then widens into a bigger lake. the third lake use to have newts in there and as far as i know was never fished .
The owners are the corporation of london and its to them any inquires should be made.
My view its a waste of time fishing there !