It was around 1990 when a retired, very senior officer was giving a history lecture to a class of British officer candidates, reminding them that the 20th was the first century since the Norman Conquest of 1066 that Britain and France had never been at war with one another.

“There's still 10 years left,” came a voice from the back rows.

Britain and France are, in defense terms, the most similar countries in Europe. They spend about the same percentage of their GDP on defense and together account for almost half of military spending in Europe. Their armed forces are of similar strength (228,656 for France; 173,020 for the U.K.). They are Europe's two nuclear powers and were the main actors in the 2011 Libya campaign. Culturally, more Britons speak French than any other foreign language. Two major players in both defense industries—MBDA and Thales—are already cross-channel companies.

But the defense relationship has been fractious. The U.K has had close ties with the U.S., particularly on nuclear and intelligence matters, but France was long absent from NATO. When it came to major combat aircraft programs, Britain and Germany collaborated and France went its own way. Later, BAE Systems' transatlantic and global strategy ran counter to the Franco-German formation of EADS.

In 2012, however, it was Germany's turn to torpedo a Eurocentric industrial strategy: the EADS-BAE Systems merger. The idea made perfect sense. BAE Systems is too reliant on military sales and EADS on civilian business, notably Airbus. Both were seeking to redress the balance. But Germany, where the majority of EADS's military division, Cassidian, is based, felt threatened. Even if EADS's CEO Tom Enders is German, the answer from his government was a firm “nein”—delivered, rather embarrassingly, after the companies had declared their intention to merge.

But if “static” is the best way to describe defense cooperation in Europe's industrial sphere, that is not the case among the armed forces of France and Britain where sometimes personal initiatives, and sometimes government steps, such as the signature in November 2010 of the Lancaster House treaties, have led to a positive trend in cooperation.

One of the objectives in those treaties is to set up a Combined Joint Expeditionary Force (CJEF), composed of two contingents of 5,000 from the army, navy and air forces of each country, plus a carrier strike group. The CJEF would be at the disposal of France and the U.K. but would also be available for NATO or European Union missions.

Encouraged by this, and on the initiative of their respective squadron leaders, French and British combat aircraft units' squadrons held a joint exercise in mid-October in which—for the first time—Rafales and Typhoons flew together as Blue forces, while Red comprised French Hawkeyes and Alpha Jets.

A few days later, the two-week Corsican Lion naval exercise was held in the Mediterranean to test the ability of British and French navies and marines to work together. They were based on France's Charles de Gaulle aircraft carrier. A question mark now hangs over the feasibility of having a joint carrier strike group, because Britain's decision to equip its future aircraft carrier Prince of Wales with a ramp for F-35B Joint Strike Fighters rather than catapults means that France's naval Rafales will not be able to take off from it. (On the other hand, the U.K.'s alternative, the F-35C, would likely have been too heavy for the French carrier.)

The two nations are also cooperating on individual programs such as the Watchkeeper reconnaissance unmanned air vehicle (UAV), and have made progress on collaborating in the cyberdefense field.

Ambitions to collaborate on a medium-altitude, long-endurance (Male) UAV, and to blend the results of the French-led Neuron and U.K. Taranis unmanned combat air vehicle projects, have made less progress. In the case of a Male vehicle, German, British and French politics are entangled with competition from outside Europe. EADS tried to promote its Talarion design, but gave up the effort in early 2012. Dassault, meanwhile, has taken a two-track approach. In the medium term, it has formed the Voltigeur consortium with Israel Aerospace Industries to offer France a version of the Heron-TP, while working with BAE Systems on the Telemos project, based on the latter's twin-engine Mantis demonstrator. However, there is still no firmly identified or funded requirement.

On the UCAV side, the Lancaster House agreements led to a joint Dassault-BAE study of an operational vehicle to build on experience with the Neuron and Taranis. The two vehicles are closely similar. Both are blended wing-body “manta” configurations, they use the same engine and are intended to demonstrate autonomous search and semi-autonomous attack modes (that is, with an operator on the ground confirming the target and authorizing weapon release). Taranis is expected to fly within a few months of Neuron, which took to the air on Dec. 1.

The question is when, if ever, the U.K. and France will have the funds to develop Telemos, let alone a Neuron/Taranis-class vehicle. Both nations' tactical airpower funds are spoken for well into the next decade.

Intelligence, surveillance and reconnaissance could be an area for collaboration. With the deep U.K.-U.S. relationship on signals intelligence, it is not surprising that the U.K. chose the U.S. RC-135—named Airseeker—to replace the Nimrod R1. However, another gap problem—maritime surveillance—remains unresolved. After the Nimrod MRA4 was canceled in the Strategic Defense and Security Review of 2010, previously extant agreements with, among other nations, the U.S., Canada and Norway, have continued to fill the breach. “The idea that we—or, frankly, anybody—could afford to do this entirely on our own is one that I just do not think is realistic,” Nick Harvey, the Armed Forces minister, told the Defense Committee last May.

Nuclear issues continue to form a divide between the U.K. and France, but could intrude into European politics. Although nothing will be decided in 2013, an issue set to dominate the British psyche—and with considerable ramifications beyond the British Isles —is the question of Scottish independence. A referendum has been scheduled for the third quarter of 2014, and although polls at present suggest those campaigning for Scotland to leave the union will fail, there is plenty of time for the “no” lobby's lead to be overtaken.

The issue is of particular concern because of the questions it raises over the future of the U.K.'s nuclear deterrent. The Scottish National Party, which is likely to win an election in an independent Scotland, is avowedly anti-nuclear. Alex Salmond, the first minister of Scotland and SNP leader, has suggested that an independent Scotland would insist on the removal of the Trident missile system and submarines from its territory.

Although London is downplaying the issue—Defense Minister Philip Hammond told the BBC in late October that a “yes” vote in the referendum was not expected, and therefore no contingency planning was being made in Westminster regarding re-basing the Trident away from Scotland, it is clear that moving the Trident infrastructure is not a viable short-term option.

The Faslane base on the Clyde is undergoing expansion as part of a plan to relocate all Royal Navy submarines to the base by 2017. Faslane is already Scotland's largest employer, and cost estimates for replicating its capabilities elsewhere vary from considerable to astronomical. Similarly, the Coulport site, where missiles are stored, would need to be replicated outside an independent Scotland. Alternative sites, such as Barrow or Plymouth, would require extensive and expensive modification, which would take at least a decade to implement.

Salmond—who suggests that British Trident equipment could be moved to France or the U.S.—has noted that if Scotland refuses to host Trident, the U.K. may well end up having to decommission its nuclear deterrent.

The defense posture of an independent Scotland creates a host of issues to juggle, but the suggestion that an Edinburgh government could effectively force the U.K. into nuclear disarmament is potentially the most divisive. In evidence to (the London) Parliament's Defense Committee, Prof. Malcolm Chalmers, research director at the Royal United Services Institute, was blunt in his assessment of the political maneuvering that could take place.

“If a Scottish government said, 'Right, we want to be non-nuclear, and we want to do it now, these submarines have to be back in England by next Tuesday',” he argued, “the U.K. government would say: 'OK, you want our support to become members of the European Union; you want the Bank of England to support your currency, or to share a currency with the U.K.; you want to have free trade and you want your Scottish personnel to be able to serve with the U.K. Armed Forces: well, get real. We have needs as well'.”

Given such serious outstanding issues, expanding cross-channel defense collaboration, while promising, is not going to happen without assertive leadership.