That was at Brighton marina , I saw it there when we passed by back in August
Am I being cynical? If each one is planted in a Marina berth and used for a liveaboard then that reduces the number of available berths for boating. It also means that where the council wouldn't allow planning for houses, there will still effectively be a dwelling there, with all the associated costs to the relevant council without them getting the normal revenue from permanent dwellings.
Saw that Tollesbury have applied for 8 permanent liveaboard berths recently - wonder if some of the above will turn up there.
Well, most marinas have some spare berths, so reducing the available berths for boating isn't necessarily an issue. Note that the "pontoon homes" in the OP were described as having "unrestricted holiday home use" - this doesn't mean full time occupation, and usually requires owners to have another permanent address. As for Tollesbury, they haven't applied for 8 permanent liveaboard berths, they already have them and are now retrospectively trying to make them legal. In view of the difficulty in getting in and out of Tollesbury Marina, filling it with liveaboards might be a good idea.