London Wiki

The Lea Valley Lines are three commuter lines and two branches in North East London, so named because they run along the valley of the River Lea. They were operated for much of their history by the Great Eastern Railway.

They were part of the Great Eastern Railway, now part of the Anglia Route of Network Rail.

On 31 May 2015, services between London Liverpool Street to Chingford, Cheshunt and Enfield Town were transferred to London Overground: services between London Liverpool Street and Stratford via Tottenham Hale to Hertford East and Bishops Stortford remain with Abellio Greater Anglia.

More information on the Wikipedia page [1]. The Rail Transport in London Wiki page is [2]: there is also material on the Railfuture website [3]