More than half a million victims of domestic abuse are too terrified to come forward and report their experiences, according to provisional estimates of research that specialists hope will quantify the true extent of the crime.

Citizens Advice has conducted research over the last year that reveals a higher level of abuse than previously reported. A pilot project in nine areas across the UK, in which clients were asked a series of routine questions when seeking help with issues such as debt and housing problems, found that 27% had experienced domestic abuse at some time since the age of 16 – three percentage points more than the national average reported for all women in the latest crime survey for England and Wales.

If extrapolated across the UK, the specialists believe that could mean there are up to 540,000 more victims of domestic abuse, the vast majority of whom would have stayed silent, according to Citizens Advice, which now plans to roll out the scheme service wide

According to those involved in helping domestic violence victims, Christmas and its attendant financial pressures exacerbate relationship tensions and are a factor in aggravating domestic abuse.

Bridget Cheyne, who leads on domestic violence for Citizens Advice in the Chorley and south Ribble area of Lancashire, said: "Economic pressures, such as not being able to afford the children's presents or a decent Christmas, means that that is the busiest time of year for us."

Its bureaux have dealt with 21,000 reports of domestic violence in the last year, a 16% increase from the previous 12 months. Cheyne said that in her team's latest monthly meeting, where agencies discussed the most at-risk cases, they had 31 cases, compared with 15 during the same period last year. "The cases are coming in at a rate quicker than I have known," she said.

Cheyne added that there were still too many instances of domestic violence that were discovered too late. One example, she said, was the murder of Judith Maude, 57, during the summer. Maude, of Hoghton, Lancashire, was stabbed three times in the neck and once in the back by her husband during a savage attack, yet there had been no indications or calls to the police that her husband was capable of violence. "There was no indication that she was in any danger and that, sadly, can happen if people feel they have nowhere to come forward," said Cheyne.

One victim is Karen Hanna, 38, of Chorley, who was held hostage in her home for more than a week by a partner who raped her and beat her severely. Hanna, who agreed to waive her right to anonymity in order to encourage other victims to come forward, said her ordeal began in Bristol in 2010 with a man she knew, though she had no idea he had a history of violence against women.

She said: "I was only with him for two weeks when he beat me up and I had him arrested. I dropped the charges, but he was already under licence for violence, so they put him in prison for two years." Although Hanna subsequently moved to Lancashire, her attacker's solicitor provided her new contact details, underlining last week's calls from the Labour party for victims of domestic violence to be allowed not to have to disclose their personal information because of the risk they will be attacked again.

"The day after he got out of prison, he came straight to my flat and took me hostage. He took my phone; he took my keys. I endured eight days of being held hostage, raped, battered senseless. He ripped out half my hair. I had to admit to sleeping with people that I hadn't because of his paranoia. If I admitted to doing these things, he wouldn't beat me up as much. I could only go outside with him and had to pretend everything was OK."

One night she escaped while he was drunk and asleep. "I ran out, locked him in and called the police, who have been fantastic."

Like many victims, Hanna recognised the difficulties that victims face in coming forward to ask for help. "It's embarrassing, humiliating; you don't believe that anyone will believe you."