Yes, of course: JETFERRY ONE (IMO 7923249) and JETFERRY TWO (IMO 7923251). Must have lost concentration.

David, thanks for this, but are they called Jetfoil or Jetferry?
Anyway, I found a third shot, showing her in the distance coming from Rotterdam, at speed so out of the water. Apparently she slowed down to pick up/or deliver a pilot and then sailed on. This may suggest that she had been taken on a ship loaded in Seattle, discharged in Rotterdam and prepared there for her service. Dates of the photos are definitely after the Flying Princess period, because I had no camera in in 1977-78.

FLYING PRINCESS (IMO 7932898), Jetfoil 929-100 series, was chartered by P&O to run an experimental service Pool of London-Zeebrugge 1977-1978. She was due to have a running-mate FLYING PRINCESS II (IMO 7932903), but I am not sure whether that ever entered service with P&O. The livery on this first one was a little different (see Tony's photo)

In 1980 P&O tried again with a pair of leased craft, running from Pool of London to Ostend, but that service only ran until the end of 1982, with JETFOIL ONE (IMO 7923249) and JETFOIL TWO (IMO 7923251). I am sure that the photo is one of these two, but I do not think that it will be possible to differentiate them in this photo.

Interesting that the photo should be at Hook of Holland. That suggests that it was taken at the beginning of end of their service when being shipped from Seattle or to Hong Kong respectively (there is a photo in the P&O Fleet History of JETFERRY TWO being lifted by an unidentified floating sheerlegs, quite possibly in Rotterdam.

In the meantime I checked another shot, where the bow of thePrinses Beatrix is visible, so the shot was taken much earlier than the 1988 I originally thought.

Jüergen, apologies, credits should have gone to you for supplying the wiki link.

As I will probably have taken this shot after mid 1979 and there are four P&O Jetfoils listed in the Wiki link (Thank you Tony), I guess the most likely candiates are Jet Ferry I and Jet Ferry II, but I have ideas about their deployment after delivery.

I agree with Bob. I have just posted a photo I took of the P&O vessel passing Gravesend in 1977. See http://www.shipspotting.com/gallery/photo.php?lid=2593319

Could be the FLYING PRINCESS that ran for a short time to Europe from the Thames.

Regards

Bob

@Pieter
looks like a Jetfoil 929
https://en.wikipedia.org/wiki/Boeing_929

Rgds. Juergen