For those of us brought up after the advent of antibiotics, it is hard to comprehend just how miraculous they seemed when first introduced in the forties and fifties.

Before that simple cuts and wounds - once infected - and diseases we now think of as minor could be fatal.

But nature's law of evolution has meant that mankind has always been living on borrowed time.

Within years of their introduction, the first signs of bacteria developing resistance were observed.

Luckily other, more powerful antibiotics could be substituted for those that had lost their effectiveness.

Beginning to worry

However, it has been 20 years now since the last major antibiotic was developed and scientists around the world are beginning to worry.

Already the Public Health Laboratory in North London has collected figures that show that the number of people with drug resistant infections in hospitals in Britain has quadrupled over the past two years.

While most of these patients are successfully treated with the most powerful antibiotic around - Vancomyacin - researchers in Japan have already witnessed in test tubes the growth of a bacteria on which it has no effect.

This then is the nightmare scenario - a spread of an untreatable infection - known to headline writers and scientists around the world as the superbug.

Rapid evolution

Part of the problem has been over use. That has given the bacteria constant exposure to antibiotics - allowing their genes to evolve rapidly to develop immunity.

In the UK one recent survey suggested 15% of patients had been wrongly prescribed antibiotics by GPs in the last two years.

In other countries the situation is made more difficult by patients being able to buy antibiotics without any restrictions.

Now the UK Government has asked all family doctors not to prescribe antibiotics if they can help it.

It has said giving authority for prescriptions for antibiotics over the telephone should stop, that healthy women with uncomplicated cystitis should only have three days worth of treatment pills, rather than the normal weekly supply, and that antibiotics should never be prescribed for colds and sore throats.

Most coughs and colds are caused by viruses, organisms which are immune to the effect of antibiotics.