Re local elections in City.
Your link was to Reuters, perhaps because so few papers and no broadcasters covered it.
Just the Indy (on line only) and the Financial Times.
Where was the Mirror and Guardian?

Perhaps this from the Indy adds some perspective to the "historic win."

"The Council has historically been dominated by independent councillors as the main political parties have tended not to field candidates in City elections.
However, Labour routinely contests some wards and in today's election the party increased its representation from one to five.
The remaining 95 seats were taken by independents or candidates with no party description.
http://www.independent.co.uk/news/uk/politics/labour-city-of-london-election-vote-independence-jeremy-corbyn-a7649221.html