I'm a member of Dignitas, not because I am planning imminently to travel to Switzerland to end my life, but because of the provision of Patient's Instructions that are legally binding: this allows also for decisions to be taken if I should be no longer able - owing, for example, to an accident - to be taken. I feel better knowing that should I undergo, say, a severe brain injury, that my wishes in this circumstances are recorded and will be respected.
The issues surrounding legalisation are very complex, though, as PP have said, particularly when the onus might be on the state itself to take decisions. In practice, it's my understanding that in most cases, it is not found in the public interest to prosecute those who help family members to travel to Dignitas - and anyway, you need to be physically capable of taking the drugs yourself, as well as of sound mind to consent: so arguably, people are already "dying before they are ready" not because of British law over being accompanied, but because of restrictions in Swiss law.
A PP mentioned that prescribing drugs with the knowledge that a side effect might be death is legal (as opposed to prescribing them to die): I know of a number of cases in the past where this has happened, but I'd be interested to know how common it still is.
Also - dying can be extremely lengthy, even when someone is ready to go: and not everyone is in physical pain at the end of life - I think this is an enormous issue to legislate for, and I don't see it happening quickly: not because, as some people have said, over squeamishness over death, but rather closing every loophole possible to ensure that there is as little potential for abuse as possible.