Using Bluetooth Phone I Assume Its Not Breaking Law

[kenali]

why driving

[Buenchico]

The relevant only prohibits the use hand-held phones but that includes any phone which might need to be temporarily hand-held in order to make or receive a call. (" . . . a mobile telephone or other device is to be treated as hand-held if it is, or must be, held at some point during the course of making or receiving a call or performing any other interactive communication function"). So even if you only need to hold a phone in your hand to press the 'Answer' button it's still illegal to use it while driving:
http://www.legislation.gov.uk/uksi/2003/2695/made

However a driver could still be prosecuted for using any type of phone if the police (and CPS) believed that it could be shown that, by doing so, he wasn't in proper control of the vehicle. ("No person shall drive or cause or permit any other person to drive, a motor vehicle on a road if he is in such a position that he cannot have proper control of the vehicle . . . ")
http://www.legislation.gov.uk/uksi/1986/1078/regulation/104/made

He could also be prosecuted for failing to exercise 'due care and attention' if the police/CPS thought that the circumstances merited it. ("If a person drives a mechanically propelled vehicle on a road or other public place without due care and attention . . . he is guilty of an offence")
http://www.legislation.gov.uk/ukpga/1988/52/section/3

[Buenchico]

^^^ There seems to a word missing in my first line!

"The relevant legislation only prohibits . . . "