Almost half of those aged 65 and over are unable to use the internet safely and successfully, according to new research.
Age UK said analysis found that 46% of older people could not complete all eight of the most fundamental online tasks around using the internet.
The charity has warned that the move to make more public services online by default could be excluding millions of older people from being able to access essential services.
The study found that 23% cannot turn on a device and enter any account login information as required, while 28% are not able to find and open different applications.
Similar numbers are also unable to keep their login details secure, update or change their password, adjust device settings to make usage easier, use controls such as a mouse or keyboard, or find, open and use a website.
Meanwhile, 35% were not able to set up a wifi connection on their device.
According to Age UK analysis, although the number of older people online has increased substantially in recent years, there are still around 2.7 million older adults in the UK who do not use the internet at all.
Caroline Abrahams, charity director at Age UK, said: “The figures we are releasing today should be a wake-up call for policymakers, because they show the alarming extent to which the rush towards ‘digital by default’ is excluding our older population.
“It is well known that millions of older people are not online and that’s bad enough, but now it is also clear that, even among those who are online in this age group, the majority only have relatively limited digital skills.
“When you think about it, this is not really surprising since they did not grow up with the technology and some have had only limited exposure to it as adults.”
In response, Age UK has launched a new public campaign called Offline And Overlooked, which calls on public services to offer an easy-to-use, offline way of accessing key services, and urges the Government to publish an updated digital inclusion strategy to support people of all ages in getting online.
The charity said it is launching an online and offline petition to allow the public to offer their support to the campaign.
Ms Abrahams added: “The fact that so many millions of older people are unable to participate safely and successfully online is an inconvenient truth for governments and other organisations keen to slash costs by moving everything online, but it’s one we must confront and act on as a society.
“If we don’t, we are essentially saying it’s OK for legions of older people not to be able to do ordinary things like book a medical appointment, organise a blue badge for their car or pay to park it, and surely that is totally unacceptable.
“It is at best infantilising older people and at worst erecting insurmountable barriers when it comes to them getting the essential services they need – including medical treatment, which is downright dangerous.
“At Age UK we think it’s time that everyone has the right to access public services offline.
“This is not being Luddite, far from it – as a charity we run some brilliant digital inclusion programmes around the country – but rather a recognition that online methods simply are not working for millions of older people now and never will, and they should be able to choose to access public services in more traditional ways – by phone, letter and face to face, as appropriate.”