This was one out of four films with Michael J. Fox in them that came out in 1985. (Family Ties Vacation, Teen Wolf, Poison Ivy, and Back to the Future.)
Came out the same year as National Lampoon's European Vacation (1985), with many similar plot points.
Not on any streaming services, but available on the season four dvd set in the bonus features.
In the 2001 interview with Archive of American Television, star Michael J. Fox described it as a "debacle".
The Keatons fly to London on the now-defunct British Caledonian Airways. The airline was acquired by British Airways in 1987, and continued operating as a charter service under the name Caledonian Airways until the year 2000.