I wonder why there would be a British policeman in Lisbon?

Perhaps he was connected to the embassy, or he was sent over to guard the wreckage, to safeguard any evidence for the investigation? Just guesses I'm afraid.

It is surprising how often casual trial/test etc events that come to grief turn out to have unexpected passengers on them. The French high-speed train crash at Strasbourg, and the German Maglev train crash both had this. The Russian Sukhoi Superject in Indonesia 10 years ago likewise, and there have been others in the past.

Maybe the photo wasn't taken in Lisbon? There's at least part of a letter 'V' painted on the large piece of what looks like a wing (although it could be part of an 'A' upside down, the reg being G-AFCK painted on camouflage) and at least 3 guys near the bobby are wearing ties, hardly the sort of garb for the Portuguese but common in the UK.

British personnel sent to investigate the crash or embassy staff?

That's what I thought too, but the best I can do is this cropped bit from the second photo. I can see 'LISBOA' in the second line, although it's a stretch, which would support the photos having been taken in that country, or next to a barge that hailed from that country. If they shipped parts over to the UK, I would have expected a vessel that was a bit more substantial though.

https://cimg5.ibsrv.net/gimg/pprune....ad8955ff71.jpg

It's the third photo containing a bobby and three 'official' looking types wearing ties that, to me, is not Lisbon and is more likely to be in the UK; I don't dispute the other photos.

I find it hard to believe that the wreckage would have been repatriated to the UK in the middle of a war.

I don't think that happened; what I'm suggesting is this third photo is of an entirely different crash somewhere around the UK (unlless they wore that type of police uniform in Malta)

Malta? Isn't Lisbon in Portugal.

Maltese police wore that style of police uniform including the helmet; I think they changed to khaki later but I don't when; there must have been quite a few flying boat crashes there during WW2.

I believe the Maltese stopped using the British "Bobby" type of uniform well before the second war.

But these pics come from the National Archives file on G-AFCK

Embassies generally are "guarded" and I wouldn't have thought that we could spare or need a platoon or whatever of armed servicemen.

As Portugal was neutral, and our oldest ally, I wouldn't be surprised if UK policemen were part of the embassy staff.

Obviously not there then!!

As bean has said the photos come from the official file of the G-AFCK accident, proof enough. The second photo is the underside of the tail boom with attached stabiliser, the third photo is of the upper fuselage between the wing trailing edge and fin, identified by the circular hatch, located immediately forward of the letter K of the registration in the first photo.

Now if we could only identify the policeman!

My wife's father spent 2 years as an army corporal in WW2 'guarding' the embassy (or maybe it was the High Commision) in Jamaica so at least in some cases, it did happen.