While IIP&O was an early user of both the VC7 and later the VC10, they did place an order for a small number of 707-420s in the late 50s to fill the gap between the production of the two aforementioned airframes (The VC7 was too heavy and inefficient, and combined with the engines being embedded in the wing, it was not a completely popular aircraft).
The 727 was also a very popular airframe (due to the third engine allowing over-water flights - California doesn't follow modern EETOPS rules, and limits the engine-out divert distance for twinjets to just 60 minutes of flying time, but the 727's third engine means that it is able to avoid such restrictions). Shown here is an IIP&O 727-200 with Conway engines (placing it early in the carrier of the airframe, as many of the later airframes got more efficient engines).