1) The aforementioned statue is on top of a 130ft high column, so anyone wishing to do anything to it is going to have to bring some fairly serious climbing equipment.
2) Earl Grey was the Prime Minister when Britain abolished slavery throughout the Empire, so I can't imagine his statue is likely to be on anyone's agenda to topple as far as BLM goes.
I wouldn't count on it!
There are some out there who are very keen not to hear anything about Britain abolishing the slave trade! Hopefully the 130 foot column will provide a sufficient disincentive........................