Nearly two-thirds of people with asthma are still not receiving the basic level of care despite claims it could prevent two out of three asthma deaths a year, according to a survey by Asthma UK.
The study revealed a "frustrating" lack of progress in asthma care, following similar findings last year.
Donna Green's son Tiernan was one of the UK's 1,200 asthma deaths in 2017.
"As a mum who has lost a child to an asthma attack, I don't want any other parent to go through what we have."
Donna, of County Armagh, added: "I didn't realise how serious asthma was, and I found out in the most devastating way, when my boy died in my arms."
According to the survey, Northern Ireland had the best performance for basic asthma care across the UK, with 48.2% receiving basic care - and Donna maintains that Tiernan had been receiving satisfactory support for his asthma.
At his inquest, the coroner said Tiernan had an asthma review lined up with his nurse, but tragically died before he had the chance to go.
Yet Asthma UK's annual report - which surveyed 7,611 people - found that only 35% of patients with asthma in the UK are receiving the most basic level of asthma care.
Basic care involves three key elements, as set out in national guidelines. They are:
- a yearly asthma check-up
- a written asthma action plan
- a lesson in how to use an inhaler
There are 5.4 million asthma sufferers in the UK, including 1.1 million children.
Based on the proportion of people in the survey who responded - and applied to the UK's asthma population as a whole - the charity believes 3.5 million asthma sufferers are not receiving basic care.
A lack of basic care can be fatal. NHS data from the past four years shows, on average, someone is admitted to hospital for an asthma attack in the UK every eight minutes.
Tiernan, was 20 when he died.
"Tiernan came to my bedroom door, having an asthma attack, gasping for breath. He was pale, his lips had turned blue and he was taking his inhaler but it wasn't helping," said Donna.
"I called an ambulance and was on the phone when he turned to me and said, 'mum I'm going to die tonight'. It was the most frightening moment of my life.
"Tiernan collapsed on the floor and stopped breathing and I gave him CPR while my daughter continued talking to the paramedics, but he died before he got to hospital.
"Losing Tiernan has left a big hole in our lives."
Donna has joined forces with Asthma UK to campaign for better care.
"Mums often tell me that doctors are brushing aside their worries about their children's asthma and they aren't being given what they need."
Statistics show that asthma patients are four times more likely to be admitted to hospital for asthma if they don't have an asthma action plan.
The use of written action plans has increased year on year since the Asthma UK's first annual survey in 2013, with nearly half of those surveyed in 2017 (43.9%) saying they now have have a written plan for managing their or their child's asthma.
However, the 2017 survey found annual asthma reviews and inhaler technique checks have dipped.
One in six people (15%) with asthma - an estimated 800,000 - said they received poor care, with wide variations geographically.
While Northern Ireland recorded good figures, only 27% of sufferers in London and 26% in Wales received basic care compared, to the UK figure of 35%.
The survey also found marked generational differences. A quarter of people aged 18 to 29 (25.1%) received basic asthma care, compared to 41.7% of people aged 70 to 79.
Dr Samantha Walker, from Asthma UK, said: "There's a postcode lottery with millions not getting basic asthma treatment, despite the fact it is proven to save lives.
"It shouldn't matter where you live - people with asthma should get a written plan to help them manage their asthma, a yearly review to check their medicine is working and help to ensure they are taking it properly."
Dr Imran Rafi of the Royal College of GPs said: "This report recognises that we need better information sharing between primary and secondary care to improve the outcomes of patients with asthma, and we agree that this process needs to be more seamless to ensure patients are receiving the best possible care throughout.
"It is also vitally important that patients understand their treatment and how to properly use equipment, such as inhalers, and we support any measures that encourage patients to feel more confident to manage their condition effectively and appropriately."
An NHS England spokeswoman said: "GPs are best placed to provide appropriate asthma treatment and we are rolling out support to help them improve the diagnosis and treatment of the condition, including the development of local hubs that will make testing more effective."