Jeremy Hughes, chief executive of the Alzheimer's Society, accused the Government of an "empty promise".
He said: "People with dementia and their carers are being forced to pay a dementia tax of tens of thousands of pounds a year for essential care and support.
"To them and thousands of other vulnerable people, an agreement in principle to a cap on care costs is meaningless.
"This empty promise also ignores the separate problem of underfunding of care as a whole. Some people are struggling with no care and no assets - for them, a cap on costs is useless.
"Further bickering between politicians will be a catastrophic failure of political leadership as families continue to struggle to care for people with severe disabilities.
"It is time for all parties to commit to a real public discussion about how we pay for the costs of care and make the costs for families fair. We cannot afford to delay any longer."
More top news
The Cosby Show star, 80, was found guilty of three counts of aggravated indecent assault.
The Government's stance risks a negotiating car crash with the EU, as it refuses to acknowledge risks over the Irish border.
Sunshine and a soaking