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Offered by the Brighton & Hove Bus Company and costing £15, the tour promises to show people sights including Epping Forest, Heathrow Airport Terminal 5 and the Dartford River Crossing bridge.
In addition, a commentary hopes to provide "a whole host of fascinating facts" about Europe's second largest ring road.
"We're keeping it as a surprise whether we'll travel clockwise or anti-clockwise," says the M25 Orbital Tour webpage.
"But suffice to say, all the great opportunities to see the amazing sights around this iconic motorway will be available."
The company also promises a bottle of champagne to the person who guesses closest to the distance of the trip.
Though April has been fully booked, it is still possible to buy a ticket for the May and October tours.
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