The controversial muscle-freezing drug botulinum toxin A, has been identified as a highly effective cure for incontinence.

A consultant urologist from Edinburgh has performed experimental bladder injections on around 100 private and NHS patients and says it is so successful it should be offered on the NHS. But the procedure is uncomfortable, involving around 25 injections into the bladder; women who have undergone it say it has changed their lives.

The new procedure starts with patients receiving a local anesthetic and then a flexible tube called a cystoscope containing a camera and a needle is inserted into the bladder via the urethra. The toxin works on the nerve ends in the bladder, blocking signals to the muscles.

Although the drug is shown to be effective cure for incontinence with no major side effects, there are a small number of patients who will have an "exaggerated response" which means they will be unable to pass urine at all for a few weeks and will be forced to use a catheter.

Critics have welcomed the development but are concerned about the use of the drug without a licence.

Mary Scanlon, Scottish Tory health spokeswoman called for further testing: ‘While this development is very welcome, I would want to know it has satisfied all criteria and has been granted a licence. This is a toxin and I would want to know the long-term effects of this procedure before it is made available on the NHS.’

Botulinum toxin is the most potent neurotoxin known to humans; just one gram is capable of killing a million people if inhaled. It is currently approved for cosmetic procedures and medical conditions such as strokes.