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At the current time, assisted suicide is still illegal in the UK, principally because a large majority of the people who would have to enact any change in the relevant legislation consider themselves too important to ever consider suicide, assisted or otherwise.
Until the limits of responsibility are clarified in law, it is probably prudent to refuse help or encouragement to anyone wishing to kill themselves, unless your refusal itself may plunge the potential suicide into even greater despair and prompt them to kill themselves before you have finished explaining why you can’t help.