Janette Scott arrived at the location on Taggs Island in a brand-new sports car, a 21st-birthday present from her husband Jackie Rae. Rehearsals started with Ian Carmichael driving a Bentley with faulty brakes, which he only found out were faulty when he went into Janette's car, causing a large dent.
In the scene where the old houseboat moves downstream at a rapid rate of knots and accidentally careers through a pontoon carrying half a dozen people, landing them all in the water, the boat continues and runs down several other small sailing crafts. The director seems to have resisted the temptation to speed up the film for comedic effect, as was so often done in older movie scenes of this type. It is clear that the other participants in the chaotic scene are playing it authentically and in real time, demonstrating that the old tub actually has an impressive speed. Later scenes of the houseboat traveling along the River Thames show it proceeding at a much more sedate pace--a strict requirement of the Thames Authorities.