Cat Smith at Labour List writes that tasers are dangerous, possibly illegal, and should not be used. This comes after a man died after being hit by a taser 3 or 4 times. However, she admits that the last time the IPCC felt the need to investigate the death of someone after they were hit by a taser was in 2006 and in that case it was ruled that the taser was not the cause of death.
According to the Home Office tasers have been used 8,599 times between 2004 and 2010. And yet no one died because of tasers in all that time. And if a taser doesn't kill you it does no lasting damage. Compare that to a baton which can cause death (has caused death) and also causes lasting damage every singe time it is used.
To add some context, according to this site 143 people died while being chased by police and 215 people died in custody between 2004 and 2010.
UPDATE: This report from the IPCC (pdf, section 7 on page 3) confirms that since 2004 only one case involving death was investigated with respect to the user of a taser and it was concluded that the death was not attributable to the taser use.