Peter Saunders, chief executive of the National Association for People Abused in Childhood (Napac), said the charity he founded in 1995 has six weeks to find new premises, after its current landlord raised the rent by 50 per cent; otherwise, it will become homeless.

Theresa May, the Home Secretary, was told of the charity's plight during a two-hour meeting at its office last week. "I told Ms May we will be homeless because our landlord has pushed the rent up so much. I don't know where we're going to go," Mr Saunders said. "We need help. Our costs are going up, our workload is going up, and we're on the rocks. If we don't find extra funding soon then in a few months' time it could be curtains for Napac."

The charity has played a leading role in influencing the Government's wide-ranging child sexual abuse inquiry, but will have to cut staff and services if affordable premises are not found quickly.

"It's very difficult for an organisation like ours to show exactly what kind of measurable impact we have; we're much like the Samaritans in that respect, so it's more difficult for us to tick the boxes of groups who consider funding us," Mr Saunders said.

Napac's income fell by more than £100,000 between 2011 and 2013 while the charity's spending increased by £75,000, according to its accounts. Its workload increased dramatically over the same period: in 2011, the charity answered 2,902 calls and responded to 750 emails. By 2013 those figures had risen to 5,192 and 1,858 respectively. The charity recently opened a new office in Stockport, its first outside London, to help cater for the 300 per cent rise in people asking for support.

Mark Samaru, a leading campaigner for improved treatment for abuse victims, described the charities crisis as "insane". "To lose Napac as a national first point of contact would be akin to barring people from accident and emergency departments, shutting down the Samaritans, and then sending victims down the mines with a budgie in search of help. The situation is insane; it's the first point of contact for so many people who are disclosing abuse for the first time – they are as vulnerable as if that abuse happened only yesterday.

"If Napac disappeared, then the problem would probably go away from a statistical point of view, as victims would no longer have a national helpline to log their calls. The farce is compounded when one considers that the lifetime cost of treating an abuse victim is akin to that of a stroke victim, thus the 5,000-plus callers equate to an NHS cost of in excess of £500m. The true cost, however, is in victims' lives," Mr Samaru said.

Mr Saunders was critical of help promised by the BBC following a series of abuse scandals, including those involving Jimmy Savile and Stuart Hall. After the Savile scandal erupted two years ago, George Entwistle, the former BBC director general, gave Napac £10,000, which was used to help train staff to handle calls from abuse victims. Calls spiralled after the allegations against Savile were revealed.

A row between the charity and Lord Patten, the former BBC chairman, became public when letters between the two were published. It was resolved when Lord Patten acknowledged Napac's important role and the BBC's "essential" relationship with organisations such as Napac as it "seeks to deal with the fallout from the appalling crimes carried out by Jimmy Savile. I hope our two organisations can continue to work closely in the future".

Despite this, Tony Hall, the current director general, decided to postpone any further contact with Napac until after the review by Dame Janet Smith into abuse at the BBC is completed. No date has been given for the publication of her report about the Savile and Hall years, but it is expected early next year.

Mr Saunders said: "We met a year ago and Tony was very pleasant, but he said he wanted to wait until the New Year to take things further. I just hoped that we would have had some more contact, with a view to some more support.

"I'm often at the BBC and the staff are brilliant. People say 'We have a lot to answer for, with Savile and other monsters who thrived under our watch.'"

• South Wales Police will lead an Independent Police Complaints Commission (IPCC) investigation into allegations of "a criminal and misconduct nature" against police and council officials in North Wales, The Independent on Sunday can reveal. The IPCC launched the investigation, named Operation Orarian, after complaints were made against North Wales police officers and officials from the former Gwynedd County Council about their handling of child abuse allegations in 1986-87 and 1991-93.

A South Wales police spokeswoman said: "South Wales Police have been appointed to investigate these complaints. It is anticipated that the investigation, Operation Orarian, will last a minimum of six months."