Stories of betrayal, bribes and stolen documents make for racy tales with all the elements of spy fiction.

But the truth is that nothing in the Berlin case should surprise us. What is alleged to have happened is not very unusual, even if we do not hear about it very often.

In recent years, Western states have called out Russia for the aggressive actions of its intelligence services - for instance the GRU, Russian military intelligence, using nerve agent in Salisbury or blowing up an arms depot in the Czech Republic, both actions killing innocent people.

But you will not hear the same complaints when it comes to the allegation involving the British Embassy in Berlin.

That is because if it turns out to be true, following the legal process, then it would be business as usual when it comes to more traditional spying.

And also, although they may not like to admit it, because it is exactly the kind of thing that Britain's MI6 and America's CIA regularly do in Russia as well as other countries.

If the authorities' suspicions are correct, the methods and targets in this case were decidedly old school.

Cyber-spying, stealing secrets remotely, has certainly become more dominant since the arrival of the internet. There was a fear in MI6 in the 1990s that they would be put out of business thanks to what could be done online.

But the reality is that people still count in the spy world. People hear things that are not always put down online. They can provide access to places and other people and answer questions that documents cannot.

Spies carefully assess people who might have access to useful information and look for some weakness they can exploit.

Decades ago, the Soviet Union could rely on communist ideology to recruit people in the West but in recent years it has more usually been people motivated by cash, often overlaid with some kind of grievance or disaffection with their life or work and more rarely a sympathy with Russia.

Germany may not be the Cold War crossroads divided between East and West as it once was, but it is the economic and diplomatic powerhouse of Europe and clearly a top priority for spies with a number of recent cases there involving China as well as Russia.

The apparent specific target in Berlin was also hardly unusual. Embassies are full of interesting plans and people - for instance what negotiations are taking place over sanctions against Russia or what kind of intelligence co-operation is taking place against Russian targets.

Because they are a prime target, security measures in embassies can be intensive. Diplomats are carefully vetted and intelligence officers will work out of secure "bubbles" to make it harder for microphones to be drilled through walls to eavesdrop on conversations.

Locally hired staff - ranging from security guards, as alleged in this case, to cleaners - are subject to some security checks but they are not as intense as those for diplomats. Everyone knows there is a potential risk of them being subverted by money or some other inducement to provide information or access.

That means in Moscow, CIA officers have had to try to maintain their cover that they were "just" diplomats - even inside their own embassy compound - for fear of giving themselves away.

Spying does happen all the time, but what is fairly rare is for cases to be made public or go to trial. One reason is that the origins of the investigation are often secret - it may be that there is a spy within Russian intelligence tipping off the Brits or the Germans, but they need to be protected. Or there could have been some compromise of their communications or the way they operate - likewise, the spy-catchers would not want that to become public, so they can continue to exploit their advantage.

Bringing evidence into court can also be tricky. British security officials have recently been arguing that one of the reasons so few cases make it to court in the UK is that current Officials Secrets Act legislation is so out of date. Often in the past when a person was suspected to be working for Moscow, they would be confronted in the hope of extracting a confession, as happened with MI6 officer George Blake, or sometimes they would be offered a deal in order to avoid a trial which might be embarrassing, as happened with another MI6 officer, Kim Philby.

But even though few cases make it into the newspapers or into court, don't let that fool you into thinking that this kind of spying is not going on all the time, just below the surface and usually out of sight.