A new code for victims drawn up by the Government risks seeing up to 700,000 people who have been burgled, robbed and assaulted "fall through the cracks".
Victim Support said plans to limit automatic referral to support services will make it difficult for people to "get the help they need".
All victims are currently automatically offered support once they have experienced a crime, but in 80% of cases they do not take it up.
Under the new code, ministers have proposed restricting automatic referral to those who have suffered a "serious" offence and those deemed vulnerable by being under 18, mentally ill or persistently targeted.
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Almost a fifth of hospital patients were also unable to reach their call button, a report warned.
At least 2,400 cancer sufferers die needlessly every year because their GP does not refer them to a specialist quickly enough.
It comes after shadow chancellor John McDonnell made a surprise U-turn on the Tory budget vote which is due later today.