SPYING on friends as well as enemies has always been part of the intelligence game.

To pretend otherwise would be naive in the extreme. The trick, of course, is not to get caught.

Enter the US National Security Agency (NSA) and ex-CIA systems analyst Edward Snowden, the man behind the leaks about the US and UK surveillance programmes.

The fallout from Mr Snowden's whistleblowing reached new levels of intensity this week with claims the NSA had spied on millions of French and German phone calls, and had even monitored German Chancellor Angela Merkel's mobile phone, or "handy" as they are known in Germany.

Already many Germans have dubbed the scandal "Handyüberwachung". For non-German speakers it doesn't exactly trip of the tongue, but is an effective catch-all phrase that neatly sums up the activity of those tasked with keeping tabs on mobile phone call conversations.

For many Germans, especially those still scarred from the days of their own surveillance obsessed East German Stasi security service, all this has a disquieting resonance.

Not least among them of course is Chancellor Merkel, who grew up in that very time and place. This would go some way to explaining why she lost no time in ringing President Barack Obama - and I wonder if that call was taped - to question this "serious breach of trust" and demand a "complete explanation".

German outrage was only matched by that in Paris a few days earlier when French newspaper Le Monde reported similar claims of US snooping. This led to the French foreign minister calling in the US ambassador before reading him the riot act.

Amid all these accusations and the resulting diplomatic rancour, two questions are worth considering.

The first concerns the true extent of US intelligence surveillance operations. Just how widespread are they? And, if as appears to be the case, the NSA has been actively intercepting telephone calls and email traffic of friendly nations and allies, what might the diplomatic implications of this be?

To take the scale of US ­operations first, it's probably fair to say a pretty good picture of this can be gleaned from the US government's top secret fiscal breakdown, known as the "black budget".

Ever since 2007, Washington has annually released its overall level of intelligence spending. What it has not readily opened to public scrutiny, however, is how it uses the money or whether the expenditure matches up to the goals set by the President and Congress.

All this changed recently after the Washington Post obtained from Mr Snowden a copy of the $52.6 billion "black budget" for 2013.

According to the newspaper, the 178-page budget summary for the National Intelligence Programme reveals the "successes, failures and objectives of the 16 spy agencies that make up the US intelligence community", and outlines the cutting-edge technologies, agent recruitment and ongoing operations involved.

Among some of the most ­interesting revelations in the document are the following. First, spending by the CIA is way greater that any other US spy agency, including the NSA, often regarded as the giant of the community.

Second, both the CIA and the NSA have begun aggressive new efforts to hack into foreign computer networks or what is known as "offensive cyber operations".

Third, and perhaps most ­significant in terms of the current French and German surveillance claims this week, the US intelligence community takes an equally active interest in friends as it does foes, including Israel long regarded as a US ally, but a nation with a track record of espionage against the US.

While this targeting of friends might come as a surprise to the lay person, within the intelligence community it barely raises an eyebrow. As a newly declassified intelligence document reveals, the NSA and its predecessors have long been doing just that.

According to Matthew M Aid, a leading American military and intelligence historian, the NSA's intercept operators monitored French military communications in Indochina in the 1950s and much of what the US intelligence ­community knew about the Israeli nuclear weapons programme in the late 1950s and early 1960s came from intercepted French communications.

More recently, when the French government dug their heels in over US and British plans to invade Iraq in 2002 and 2003, the NSA had their surveillance ear very close to the ground in Paris.

This week White House ­spokesman Jay Carney's assurances to Chancellor Merkel that the US "is not" monitoring and "will not" monitor her communications was tantamount to confirmation through omission that in the past it has.

Knowing now as we do from the likes of the "black budget" that the US spy agencies have vastly expanded their intelligence-gathering capacity since the attacks of September 11, and appear to have been caught in the act of watching friendlies like France and Germany, brings us to the question of what the long-term diplomatic implications of this might be.

Here, analysts are a little more divided. In a New York Times editorial, columnist Roger Cohen made the case that "a backlash could see Europe limit its sharing of financial and other data with the US or impose heavy fines on American telecommunications companies that pass on European user details." The word "ally", he wrote, "is beginning to feel like a 20th-century idea that has lost its relevance".

There may be some truth in this. But in Washington, London, Paris or Berlin, the current heat over the surveillance fallout will dissipate in time.

In the counter-terrorism arena and faced with the global threat posed by jihadist and other groups, there is more to be gained from collaboration among these transatlantic players than from throwing diplomatic rattles out of the pram.

At the end of the day the concept of friends and enemies is a fluid one in the intelligence world. Targets, as they say, are far more important.