The study found that over a third, i.e. 37 percent, who reported not checking their breasts regularly said they did not know how to check - or what to look out for.
A campaign is being launched by Breakthrough to encourage more women to check their breasts regularly for changes, and to report anything suspicious to their doctor.
Early diagnosis of breast cancer offers the best chance of successful treatment.
"We know that the earlier breast cancer is diagnosed the more likely it is that treatment will be successful. Checking your breasts isn't complicated and there's no need to follow a fancy routine," BBC quoted Dr Sarah Cant, from Breakthrough, as saying.
"Just be familiar with how they look and feel normally," she added.
The survey also revealed widespread confusion over what signs to look out for when examining the breasts.