It wasn’t so long ago that people with autism were thought of as Rain Man-type rarities, individuals whose behaviour was so odd - like the character played by Dustin Hoffman in that 1988 film - that they were not only few and far between but also instantly recognisable.

Now we know it’s not that simple. The autism spectrum encompasses people whose condition manifests itself in a variety of ways. It is thought one in 100 - but perhaps more - people in the UK has autism with huge numbers undiagnosed, many of them adults who grew up at a time when the condition wasn’t widely recognised.

They may have faced life-long struggles fitting into a ‘neuro-typical’ world when their brains are wired differently. Many will also be women, who may have been under-diagnosed, perhaps because they are better at ‘social masking’, or copying non-autistic people’s behaviour in order to fit in.

Ipswich grandfather Ian Hartley, a public governor of the Norfolk and Suffolk NHS Foundation Trust (NSFT), recently walked 10,000 steps every day to mark World Autism Awareness Week and raise money for charity. He became aware of the special needs faced by people on the autism spectrum during his induction at NSFT, which runs the Suffolk Autism Diagnostic Service. “The more I thought about it, the more I realised that various people I’ve known over the years are probably on the autism spectrum,” he says.

Many of us can relate to that. We all know people whose behaviour baffles us, who seem to say the ‘wrong thing’, appear blunt or rude. Of course, they may just be rude. But it could be something else. Maybe some of us even recognise those traits in ourselves.

“Autism affects people from across society,” says Dr Colm Magee, clinical lead and psychologist with the Stowmarket-based Suffolk Autism Diagnostic Service adult team. “They are of all kinds of intelligence and background, they might be specialists in their field but struggle with the politics of working in an office environment. Things like office humour and banter can feel very personal; they don’t know it’s only a joke. They take things more literally and if they try to do banter it can go horribly wrong.

“Every interaction for someone with autism is like a job interview. They have to remember to make eye contact, decipher what the other person means and understand the conversation. It can be exhausting.”

Often, they can withdraw or seek refuge in narrow, perhaps obsessive interests.

Although there are many differences in how autism affects people there are also common features. It’s a life-long neurodevelopmental condition affecting how a person interacts, communicates and makes sense of the world. Very often, those affected will have heightened sensitivity to sound, light and texture and find change difficult, even distressing.

Rooms at the Stowmarket centre are kept quiet and simple to avoid sensory overload and diagnosis takes in a range of subtleties. It is not just a tick-box exercise. Not everyone who finds it difficult to make friends has autism and seemingly autistic traits might, in fact, be due to something else, such as a traumatic childhood experience. “Our job is to decipher all this,” says Dr Magee.

About 65-70% of those assessed are diagnosed with autism but around 25% of referrals are not offered assessment as there is not enough information to indicate autism or other issues explain their difficulties.

“This condition is lifelong,” says Dr Magee. “There has to be a pattern from early childhood: they’ve never done imaginative play, only ate certain foods, not been able to cope with change, always had sensory sensitivity.”

The service, which covers all of Suffolk apart from Waveney, assesses around 160 adults a year. The oldest person to be diagnosed so far has been a 73-year-old man. But not everyone with autism needs a diagnosis. And not everything about the condition is negative - people with autism just think differently and that can have benefits, such as attention to detail, honesty and logical thinking skills.

“It is about how you are functioning,” says Marcina King, autism service community team manager. “If you don’t need extra support there is no need to have a diagnosis. It’s different if someone is struggling with some impact of autism on their lives or has depression or anxiety. If things get really bad at work they can find HR involved when it may just be that adjustments to their role are needed to work to their strengths.”

In those cases a diagnosis can make all the difference.

“Someone once told me: ‘It’s allowed me to be me’,” says Dr Magee. Anyone who thinks they could benefit from a referral to the service should speak to their GP.

‘They treated me as someone who mattered’

Sue didn’t find out she had autism until she was in her mid-40s and says the help she received from the Suffolk Autism Diagnostic Service transformed her life.

“To have the diagnosis confirmed made a significant difference to my attitude towards my abilities and my self-perceived failures,” she says. “It gave my partner, who was kept involved during the whole diagnostic process, a chance to learn a lot more about me, which means I have a whole new and understanding support system both at home and in my wider family.

“It also opened the way to some fantastic post-diagnostic services that have made me evaluate my life, given me the ability to arrest control over difficult phases of depression and given me new confidence. The service was absolutely wonderful. They were friendly and warm and treated me as someone who mattered, which left me feeling that I hadn’t been going slowly insane all these years. Without them, I’m not sure I’d be here today.”

More about autism

The Suffolk Autism Diagnostic Service was launched in August 2013 and is based in Haymills House, Stowmarket.

It runs clinics in Bury St Edmunds, Ipswich and Stowmarket, accepts referrals from age 11 upwards, provides short-term post-diagnostic support and directs people to organisations that can offer longer term support. The adult service carries out around 160 assessments a year and the youth service 180.

Many people with autism live relatively normal lives. Others may require more support or a lifetime of specialist support as they may have learning disabilities or other complex needs. According to The National Autistic Society, there are about 700,000 autistic people in the UK. Five times as many males as females are diagnosed but the condition is under-diagnosed in females.

Springwatch presenter Chris Packham was diagnosed with autism as an adult and has written a book and made a documentary about his life, both of which were credited with increasing understanding about the condition.