Watch Sue Perkins double the money or the Apprentice for inspiration.
I think I would focus on events. You need an idea that people will pay through the nose for.
Let's say a "wizard" themed Thames Cruise with food, a drink and kids wizard themed disco/party games.
Then find someone who has the equipment needed to fulfill your event - in this case a Thames Cruiser boat that does dining and negotiate to put on the event for 40% of ticket sales cash.
Plan and market your first event to prove the concept (selling tickets in advance so no danger you will be left high and dry) with a view to building up to daily events/twice daily /three times daily events + when your first event proves a roaring success.
Let's say an average ticket is £100 (parents more, kids less) and you build up to 60 covers each day (3 lots of 20) you are taking 40% so £2,400 each day as your share.
This doesn't take account of the fact that you need to live or commute somewhere super busy which will cost you £££ and be willing to work super hard
Also that the owner of a Thames Cruiser might tell me I have no idea how much money they already take daily and that this is not feasible as they would earn less(?) Research needed.
...not for me so I'll never be a millionaire!