Tilting at windmills was a speciality of Don Quixote, the honourably flawed Spanish man of war. Now the Ministry of Defence appears to be following in the farcical footsteps of Cervantes's fictitious knight. Wind farms, rather than windmills, are raising the hackles. Defence chiefs fear that new-age wind turbines, some of which are hundreds of metres high, will interfere with radar-based air and sea defence systems. It may render them useless.

Although easy to lampoon, national priorities of the highest order are clashing. For the sake of climate change, the Government must reduce carbon emissions. One of the more modest ambitions is that the UK should generate 20 per cent of its electricity from renewable sources by 2020. It is hoped that at least half the renewable commitment will be met from wind power. This modest target is tough enough.

Climate change obligations sit alongside the Government's basic duty to protect its citizens. Radar stations dotted along the coast of Britain are the first, and sometimes the last, line of defence against assault. Radar has revolutionised warfare, enabling soldiers, sailors and aircrew to see huge distances: round corners, through fogs and in darkness. But the turbines, says the MoD, get in the way. The problem has become acute as wind turbines have joined the mainstream. Onshore wind farms in such places as Norfolk and north Northumberland are at the centre of today's debate. Bigger offshore projects under consideration in places such as the Thames estuary will bring greater difficulties.

There is more than enough at stake to merit swift investigation. Is the MoD exaggerating the risk? Could it relocate radar stations to avoid the interference caused by the wind farms? Should the MoD have foreseen the growth of wind farms and responded by adapting security technology? If wind farms pose a genuine threat, the MoD should surely have sounded the alarm before the situation became critical. It objects to wind farm planning applications towards the end of the process. Those erecting turbines on the moors and shallow seabeds could have changed their proposals had the MoD spoken up earlier.

They still can, and they may have to. But the later the changes, the greater the cost. With money, radar stations could be relocated. Investment could be made in more powerful, or more intelligent, radar. But defence budgets are already stretched. At the same time the economic viability of wind power cannot be taken for granted. Any additional cost reduces the chance that wind will make a meaningful contribution to electricity supply this century.

Supporters of wind energy may be underestimating the seriousness of the damage done to radar signals, and the ease with which problems can be corrected. Not for the first time, they may be guilty of making overambitious claims for the potential of wind power, while countryside champions increasingly rue the way wind farms spoil sweeping vistas. For its part, the Ministry of Defence may be too Quixotic. But this is a genuine conundrum, not a laughing matter. A cost-effective solution must be found quickly. It may be a simple question of coordination and communication. If so, it is high time that different branches of government came together to avoid an unnecessary and potentially damaging conflict.