What are the average profit margins for a food seller on a busy market stall?

I am planning on opening a food stall somewhere in London, I would like to know the average profits of such traders in order to see whether it is worth-while. Any feedback would be helpful.

What is a VPN?

VPN is (Virtual Private Network) were first used by companies to enable their employees to securely access internal systems such as email remotely (e.g. from home or while on business trips). Today they are increasingly being used for personal use by individuals to protect their privacy while online in public places (e.g. when using the wi-fi connection in a cafe) or in a country where the internet is censored / blocked (e.g. China, Saudi Arabia…).