Here’s their webpage with rules for the protesters…
Harrow stop mosque building demo 13th December

BANNED FROM PROTEST

1. As with previous SIOE demonstrations, political parties are banned.

2. Any racist chanting, banners and placards will result in immediate ejection of the perpetrators from the demo as will nazi salutes.

3. Totalitarian symbols such as nazi swastikas, communist hammer and sickles, Islamic star and crescent, UNLESS CLEARLY CROSSED OUT OR DEFACED WITH A STOP SIGN.