The BBC said the documents, almost 50 pages in all, were found "in a soggy heap behind a bus stop in Kent early on Tuesday morning" by a member of the public, who wanted to remain anonymous.
Russia's relations with Washington, which cancelled the deployment of two of its own warships to the Black Sea last week after fierce Russian protests, are at a post-Cold war low.
Moscow expelled 10 US diplomats on Friday in retaliation for the expulsion of the same number of Russian diplomats from the United States over alleged malign activity.
The Saudi Grains Organisation (SAGO) said on its website it agreed to buy 295,000 metric tonnes of hard milling wheat, at a total average price of $271.05/tonne.
The government has said good weather is likely to help farmers increase their grain crop to at least 75 million tonnes this year from about 65 million tonnes in 2020.