Suddenly, the spies are back.

First we had the new Bond, then we had Restless from the BBC; in a few weeks there's a new novel from John Le Carre, and this week we have Spies Of Warsaw (BBC Four, Wednesday, 9pm) from the novel by Alan Furst.

And it seems like an inevitable trend. We've got less money because of the recession, which makes us feel anxious and paranoid – and the stage after paranoia is attack. It doesn't much matter who we attack, it could be welfare claimants or foreigners or the rich. The point is that we're feeling like we used to in the Cold War – like we have enemies again and, if you have enemies, you need spies.

Ian La Frenais, who has written Spies Of Warsaw with his old Likely Lads partner Dick Clement, has a different take on it. The reason for the resurgence in spy stories, he says, is not fear, but nostalgia for the Cold War and conflict that was much simpler than terrorism.

You can see this nostalgia all through Spies Of Warsaw, which is a pretty old-fashioned kind of spy story starring David Tennant as Colonel Jean-Francois Mercier, a French aristocrat working in Poland before the Second World War.

At one point Mercier said: "There's a new moon in two weeks," and I assumed he was using a spy code like "the canary flies tonight" and what he meant was the secret files would be delivered on Wednesday. But he just meant that there was a new moon in two weeks. In fact, Spies Of Warsaw is much more sophisticated than that, largely because of Mercier, who's a kind of Scarlet Pimpernel in reverse, heading out from France to dance with ladies in public and save men from death in private.

Tennant clearly gets the melancholia of the character (his wife has died of consumption and he's accepted the doom of loneliness) but in other ways he doesn't feel right for the role. For a start, Mercier looks reedy in military uniform, his head dwarfed by epaulettes the size of dinner plates. And perhaps because he's so thin, the moments where he kills seem to lack muscle.

There were no such problems with Mercier's German enemies. These are old-school Nazis – maybe a little too old-school in that they all looked like deviants and had no redeeming features. There was also the suggestion, as there often is, that sexually the Nazis were not the men that the Brits were. In one scene, a Nazi officer comes across a naked man with a towel held over this front. "What are you hiding, Zoller?" he says, looking him up and down suggestively. "Are you a Jew?"

It is a good one-liner, but why do we still have these simplistic portrayals of the Germans and the Allies? From the start, the atmosphere of Spies Of Warsaw was excellent –and it tightened like a ring of barbed wire as time went on – but if spy drama is nostalgic, as La Frenais thinks it is, maybe it's nostalgic for the wrong thing: the feeling of goodie versus baddie, of right against wrong, of the enemies being less human than we are.