Classified Ministry of Defence documents containing details about the British military have been found at a bus stop in Kent.

According to reports, one set of documents found behind the bus stop analyses the likely Russian reaction to HMS Defender and the ship's passage through Ukranaian waters on Wednesday.

READ MORE: Black Sea incident: HMS Defender 'fired on by Russian Navy'

More than 20 Russian aircraft and two coastguard ships shadowed a British warship sailing near Crimea on Wednesday.

The BBC reports that 50 pages, including emails and PowerPoint presentations, originated in the office of a senior official at the Ministry of Defence, were found behind a bus stop in Kent on Tuesday morning.

The papers, which have "Secret UK Eyes Only" marked on them, are believed to have been water-damaged.

Another set of documents are also thought to detail plans for a possible UK military presence in Afghanistan after the US-led Nato operation there ends.

A Ministry of Defence spokesperson told the BBC an employee had reported the loss of sensitive defence papers, adding: "It would be inappropriate to comment further."

The documents appear to show the possible routes for HMS Defender, with one route that would have kept HMS Defender away from disputed waters.  

Boris Johnson insisted HMS Defender was “entirely right” to voyage through the disputed waters around Crimea as Russia threatened to retaliate if there was a repeat of the incident.

READ MORE: Kevin McKenna: Britain’s sad little act in the Black Sea is the squeak of a failed state

Moscow claimed that warning shots were fired by Russian vessels at the destroyer as it passed through the contested part of the Black Sea on Wednesday – an assertion dismissed by the UK Government, which said only that a routine “gunnery exercise” took place.

The Prime Minister said the route was “wholly appropriate” and the destroyer was part of an international Carrier Strike Group that was “sticking up for our values”.

Addressing the press on Thursday following the incident, Mr Johnson sidestepped a question on whether he had personally authorised HMS Defender’s voyage.

He said: “These are a matter for the MoD (Ministry of Defence) but if you want my view I think it was wholly appropriate to use international waters, and by the way the important point is that we don’t recognise the Russian annexation of Crimea, this is part of a sovereign Ukrainian territory, it was entirely right that we should indicate the law and pursue freedom of navigation in the way that we did, take the shortest route between two points, and that’s what we did.”