LONDON (Reuters) - Britain’s inquiry into historical child sex abuse scandals, some involving celebrities and politicians, finally opened its first public hearing on Monday after a sleuth of problems that led to three chairmen quitting in the three years since its launch.

The inquiry is one of the largest and most expensive ever undertaken in Britain. It was set up in July 2014 by now-Prime Minister Theresa May in her former role as interior minister after a series of abuse scandals that dated back decades and shocked the public.

It is expected to take some five years to complete.

In a number of cases, victims have complained of cover-ups at the behest of powerful establishment figures including senior lawmakers, spies and police officers.

“This is an important day for the work of the inquiry,” said chairman Alexis Jay, who oversaw a 2014 investigation into wrongdoing in the northern English town of Rotherham which revealed some 1,400 children had been abused.

The inquiry heard evidence on Monday about the sexual abuse of youngsters, many in state care, who were sent to former colonies such as Australia, Canada and New Zealand under Britain’s child migration program that ran until the 1970s.

In 2010, then-British prime minister Gordon Brown apologized for the “shameful” policy which saw children being sent abroad from orphanages and other institutions, often without their parents knowledge.

Henrietta Hill, a lawyer to the inquiry, said there were “allegations of widespread and systematic sexual abuse”.

David Hill, who was sent to Australia aged 12, broke down as he detailed the suffering of some child migrants.

“Many never recover and are permanently afflicted with guilt, shame, diminished self-confidence, low self-esteem, fear and trauma,” he said, adding Britain had continued to send children despite concerns being raised.

The multi-million pound inquiry has been riven by setbacks since it began in the wake of 2012 revelations that the late BBC television star Jimmy Savile, once one of Britain’s most-loved celebrities, was also one of its most prolific sex abusers.

The first three figures appointed to lead the investigations stepped down while its most senior lawyer quit in September.

The inquiry will examine abuse at institutions including churches, schools and council bodies across Britain and will also consider whether allegations were covered up by police or politicians.

Critics say its scope is too wide, making it impossible to work effectively, while victims, many of whom have waited decades to tell their story, fear that the crimes they suffered will again be covered up by the establishment.