New York Waterway provides an extensive network of busy fast ferries on the Hudson and East Rivers from New Jersey and suburban New York into midtown and the financial district. Free buses then distribute passengers on multiple cross-town routes. Staten Island Ferry adds a substantial chunk into Battery Park and onward Subway.
But Manhattan is a 23 square mile island with 1.5 million daily commuters and the vast majority still use NY Subway, PATH and buses from the boroughs and NJ. It has the geographical limitations and opportunities for ferries to work, and the sheer critical mass of passengers. Ferry fares are quite a bit higher than a swipe on the subway or bus ticket. They still only obtain a small share of 2%, much of which from NJ into the financial district and the Staten Island Ferry. But 2% of 1.5 million is still a lot of people.
Hard to see where the passenger numbers and geographic necessity to cross a major waterway exist in the UK.
I've used NY Waterway to commute and it's the most breathtaking commute you could dream of, IMHO