Irish dancers , revellers and pets in fancy dress marched through Trafalgar Square for St Patrick 's Day Parade . Part of build up before Tuesday 's main event when 150,000 people are expected for 14th annual St Patrick 's party . Headed by former world champion boxer Barry McGuigan and features floats representing all 32 counties of London .
Irish dancers , revellers and pets in fancy dress marched through Trafalgar Square for St Patrick 's Day Parade . Part of build up before Tuesday 's main event when 150,000 people are expected for 14th annual St Patrick 's party . Headed by former world champion boxer Barry McGuigan and features floats representing all 32 counties of Ireland .