Veteran newsreader Jon Snow and actors Sir Jonathan Pryce, Suranne Jones and Vicky McClure are among 60,000 people to have signed a letter demanding 'better for everyone affected by dementia'.
The petition, which will be delivered to Downing Street today, calls for a 'bold and ambitious' plan for earlier dementia diagnoses as new research reveals many patients face crippling waits of over six months.
Alzheimer's Society, which gathered the signatures, wants a new national target to be put in place to ensure everyone with dementia receives an accurate diagnosis within 18 weeks of a GP referral, as well as a care plan and access to treatment where appropriate.
It said such an ambition has already been met for all other major health conditions, such as cancer and heart disease.
The Daily Mail revealed in June that Mr Snow had been diagnosed with Alzheimer's disease - the most common form of dementia - in 2023.
The letter urges the Government to 'set an ambitious goal to reduce the number of people that die from dementia; ensure robust plans are in place to deliver disease modifying treatments, as they become available; support the delivery of high-quality dementia training for the social care workforce; and ensure everyone can access an early and accurate diagnosis'.
The lack of a firm target means services could be cut back, with more patients left waiting months or years while their condition worsens, the charity has warned.
In some instances this could mean they become too far progressed to benefit from breakthrough drugs, which must be taken in the early stages of disease.
The Daily Mail revealed in June that Jon Snow (pictured with his wife Dr Precious Lunga) had been diagnosed with Alzheimer's disease in 2023.
The letter comes as its survey of over 1,000 UK carers of people with dementia found just under half (45 per cent) waited more than six months for a dementia diagnosis after first seeking help.
Among the 868 carers supporting someone who had received a formal dementia diagnosis, 46 per cent said the time taken to receive a diagnosis affected their work, just over a third (35 per cent) said it made it harder to plan for the future, and three in 10 felt 'life was on hold'.
Michelle Dyson, chief executive at Alzheimer's Society, said it would never be accepted for someone to be 'left to work out the next steps on their own' after being diagnosed with a disease such as cancer, but that this is 'the reality for too many people affected by dementia'.
She said: 'A dementia diagnosis can bring answers, understanding and access to the support, treatment and care that can make a real difference to people's lives.
'But we know things can be so much better.
'Too many families spend months, and sometimes years, waiting for answers while their dementia progresses. It is like trying to plan a journey without knowing where you are going or when you will arrive. Behind every delayed diagnosis is a family living with uncertainty and trying to prepare for the future without the support they need.'
The Daily Mail and Alzheimer's Society have partnered in a drive to defeat dementia, which claims 76,000 lives a year as Britain's biggest killer.
The Defeating Dementia campaign aims to raise awareness of the disease, in an effort to increase early diagnosis, boost research and improve care.
Michelle Dyson, chief executive at Alzheimer's Society, said too many people are left to work out the next steps on their own after receiving a dementia diagnosis.
Line of Duty actress and Alzheimer's Society ambassador Vicky McClure is among the signatories to the letter.
Ms Dyson previously told the Daily Mail the government's upcoming dementia plan will not be 'worth the paper it is written on' after the 18-week target was removed from a recent draft despite appearing in an earlier versions.
She also accused the NHS of treating dementia patients as 'second-class citizens' who are 'cast aside' and typically sent home with little more than a leaflet.
A Department of Health and Social Care spokesperson said: 'This Government is determined to strengthen the support that is available both to individuals affected by dementia, and the family members who look after them.
'We are bringing forward the timetable for Baroness Casey's commission on reform of the social care system, and we are appointing a new dementia tsar to help lead our work in that area, as recommended by Baroness Casey.
'We are also implementing a new action plan for unpaid carers to ensure that they receive the support and recognition they deserve for the selfless work they do.'