new Frank Hampson artwork discovered?

Browsing the Book Palace website last night, I came across this...

The link itself is here where you'll see it described thus "...This is gorgeous painting, probably used for a magazine illustration or advertisement in the late 1950s. Depicting a scene at a British port as travellers disembark from their cruise and have to face the close examination of British Customs control. It has been attributed to Frank Hampson as it very closely resembles his technique and style".

I'd go along with the Hampson attribution.
I'd go along with the magazine illustration or advert - although I wonder 2 things:
a). when would he have find the time to fit it in with his Dan Dare commitments (unless he did it when he wasn't working on the strip through ill-health)
b). is it actually a finished piece or (incredibly) 'just' a rough? The reason I say this is that only the 5 figures in the foreground of the picture look complete to me - the rest of the picture is just not quite finished to Hampson's usual high standard. The cranes in the background look particularly sketchy.

The final question then is what is it an advert for? Well, I'm assuming it's for the brand of booze that gramps has been caught trying to smuggle through Customs.
Two bottles then - I'm going to guess the one in the Customs officer's right hand is Courvoisier and in his left hand some Stolichnaya vodka.

Yours for £1250!