Over the next decade, the Alzheimer’s Society estimates that Islington will see a six per cent increase in the number of dementia cases, with the figure set to reach 1,225 by 2021. And, while Islington Primary Care Trust ranks third nationally for successful Alzheimer’s diagnoses, over 450 cases still went undiagnosed in the borough in 2010.

For Jill Batty, the first signs of her husband Dominic’s dementia came after a trip to the theatre.

The couple had been to see Shakespeare’s Measure for Measure, a play they both knew well.

But when they left after the curtain call, Dominic was sure they still had the play’s second half to come.

Six months later, the couple decided that Dominic should see his GP.

Initially, he left for the appointment alone, but returned minutes later having forgotten why he had left the house.

Jill reminded him he needed to see the doctor, but Dominic could not remember where the surgery was.

Finally, Jill accompanied him. The GP, suspecting Alzheimer’s disease, referred Dominic to a specialist.

That was 2003. Now Jill, 65, cares for her 82-year-old husband at their home in Northchurch Street, Canonbury.

And his relatively early diagnosis meant that the couple could access the help they needed before his health deteriorated too far.

Jill said: “Early diagnosis was really helpful. While Dominic didn’t like the medication prescribed, it does work for others. It also meant we could get in touch with Alzheimer’s Society for information. The local Islington group has been fantastic.”

But many sufferers in Islington are not so fortunate.

A study by the Alzheimer’s Society estimates that 39 per cent of the borough’s dementia cases go undiagnosed, due in large part to the failure of friends and relatives to spot the problems as they begin to develop.

Maggie Owolade, the Alzheimer’s Society London area manager, said: “As the number of people with dementia increases, it is vital we all take time to understand and talk about the condition.

“People with dementia and their families have told us that a diagnosis opened the door to support they wouldn’t otherwise have had access to.”

Care Services Minister Paul Burstow said: “People are afraid of dementia and rather than face the possibility that someone they love has the condition, they can wrongly put memory problems down to ‘senior moments’.

“But if you are worried, the sooner you discuss it and help the person seek support the better. Don’t wait until a crisis.

“Being diagnosed with dementia won’t make the condition worse but leaving it untreated will.”

For Mr and Mrs Batty, living with dementia is manageable. Mr Batty can be withdrawn at times, but he enjoys playing the piano and is still able to read music.

Mrs Batty added: “His memory was not what it used to be, and he soon realised there was something different going on.

“In hindsight, he realises an early diagnosis has been good. The key is to get help before you need it. I try to say that to everyone.”

n Information about dementia can be found at alzheimers.org.uk