At two points, as the school trip goes through Europe, we are shown newspaper headlines. The "earlier" paper has an April 1957 date and the "later" one a March 1957 date.
In The Belles of St. Trinian's (1954), the headmistress is Miss Millicent Fritton, whereas in this film her name is Miss Amelia Fritton, despite being the same character and being played by the same actor.
The first shot of the tow-rope between the buses shows two pieces of cloth/ flags attached to it. Subsequent shots show only one piece of cloth.
On the posters advertising the water polo match Inghilterra (England) is misspelled as 'Ingilterra'.
During the water polo scene, the Union Flag is flying upside down. This could cause people to confuse it with a Union flag flying right-side up leading to disastrous results.
Interior shots show that both of the two coaches are packed full of girls, yet after the trailing coach breaks down, everyone fits into the first vehicle.
When the buses leave St Trinian's, the leading bus knocks down the arch over the gateway. It can hardly have come in this way without knocking it down. Nor is it likely to have increased in height as it leaves laden with the girls and their equipment.