The Ministry of Defence has been forced to accept a four-day visit of military experts from Moscow under a European arms control treaty.
The visit began on Monday at Lossiemouth, international officials said, the home of an RAF quick reaction force of Typhoon jets at minutes’ notice to scramble and intercept Russian long-range bombers probing UK airspace.
Experts from the Russian National Nuclear Threat Reduction Centre will visit north Scotland as 55 warships and more than 70 aircraft and 13,000 soldiers, sailors and airmen from 14 nations gather for Exercise Joint Warrior.
Russian state media said the team from the centre, part of the country’s defence ministry, would "conduct a series of checks" at the exercise.
Sergey Ryzhkov, head of the centre, said: "During the event, the inspectors will visit ranges and plan to hold command briefings on the conducted military activities."
Sources said it was the first time Russian inspectors had attended Nato manoeuvres since relations between Moscow and the alliance plummeted after the annexation of Crimea.
Nato has withdrawn all cooperation from Russia in protest at its aggression in Ukraine, and stepped up exercises to try to reassure eastern allies who feel threatened by the Kremlin.
David Cameron said last month that the exercise would “send a clear message to those who threaten us” that the UK and alliance could protect themselves. Members are still bound by several arms control and cooperation treaties though.
The Russian team will be escorted at all times and will only be given unclassified information, the MoD in London said.
Defence sources said it was “routine” and Russian officers had last made similar official visits last year. British officers have not made similar inspections in Russia since 2010 though.
Joint Warrior is held every six months, but the current manoeuvres are the biggest they have ever been. The fortnight-long UK-led exercise will see mock amphibious landings, mine clearing and attacks by small ships, while at the other end of the UK there will be an airborne landing around Salisbury Plain.
The exercise includes submarine hunting drills led by HMS Ambush, one of the Navy’s new Astute class hunter killer submarines, and the frigate HMS Somerset.
Britain was last year forced to call in help from Nato patrol planes after a suspected Russian submarine was detected off the coast of Scotland. Aircrews, submarines and submarine warfare frigates spent weeks scouring the North Atlantic.
An MOD spokeswoman said: “This routine inspection, which forms part of our obligations under the Vienna Document 2011, will have no impact on Joint Warrior. The inspection party will not have access to any sensitive information and will be accompanied throughout."
The British Royal Navy HMS Astute (S-119) nuclear-powered attack submarine leaving Faslane.