My grateful thanks to you Roberto for giving my theory your consideration. Not late by any means! I think there are still some who post regularly to Mr Murray’s board who have not yet seen it.
I agree, my assertion “The two Russian men … were never seen anywhere near the Skripals” is a rather sweeping statement.
As you point out though, the two men were at the station when the Skripals were taken ill. And there is no evidence to connect them directly to the Skripals. There is no evidence that they met with the Skripals.
I think their story is plausible as visiting Stonehenge (which they said to have wanted to do, but were prevented by the weather) is something that any visiting tourist to the UK might want to do.