How many letters does the top answer for “city in greater london” have?

The most common answer is cityofwestminster (17 letters).

Crossword clue: city in greater london

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

cityofwestminster 17 letters wd-fact-v3

city in london 67% similar → cityoflondon

bridge in city of london 50% similar → blackfriarsbridge, blackfriarsrailwaybridge, londonbridge

city in greater bilbao 50% similar → portugalete

landmark in city of london 50% similar → barbicanestate, guildhall, lloydsbuilding