I am an Indian citizen holding a regular passport, can I apply for a Schengen visa from within the UK?
According to the website of the Embassy of Belgium in the UK
You should apply for your visa in person at the Belgian embassy or consulate which is competent for your country of residence
The rules should be similar or identical for other Schengen countries.
Thus, if you can apply in the UK only if you are a resident of the UK.