UPDATED 12.39PM: New Zealand judge Dame Lowell Goddard has abruptly resigned as head of the independent inquiry into child sexual abuse in the United Kingdom.

LISTEN ABOVE: Advocate for those abused by the Clergy and core participant in the inquiry, Phil Johnson spoke to Newstalk ZB

LISTEN: Judge Lowell Goddard speaks to Newstalk ZB in 2015

No reason was given for her resignation.

Dame Lowell, 67, was appointed in February 2015 to lead the inquiry following the resignation of two previous chairwomen.

Her resignation letter, which was posted to the home secretary's website, contained just two lines.

"I regret to advise that I am offering you my resignation as Chair of the Independent Inquiry into Institutional Child Sexual Abuse, with immediate effect. I trust you will accept this decision," Dame Lowell wrote.

In her reply Home Secretary Amber Rudd acknowledged it would have been a difficult decision to make but it was the right one.

She thanked Dame Lowell for her work and commitment to the role.

"You have consistently demonstrated your desire to leave no stone unturned in order that the voices of the victims might be heard," Ms Rudd said.

"It is a testament to your commitment that you have taken the difficult decision to stand down now, having set the inquiry firmly on course, and allow someone else to lead it through to the end.

"With regret, I agree this is the right decision."

In a separate statement, Ms Rudd said: "I want to assure everyone with an interest in the inquiry, particularly victims and survivors, that the work of the inquiry will continue without delay and a new chair will be appointed."

Waikato University professor Alexander Gillespie acknowledges she has come in for a lot of flak in the UK for the amount of money she was being paid, and travel perks she was receiving.

But he doubts that would be why she's walked away.

"Judges and people at the top of their game, and she's at the top of her game, do get paid a lot and if you want to move down the scale of what you could pay people, you're going to lose integrity of that position."

There's been criticism Dame Lowell wasn't up to scratch with British law. At one point she even admitted to barristers that British law confused her.

But Mr Gillespie said this would have been the case for anyone pulled in from outside the British legal system.

He said they needed someone from outside the country, after two British chairs of the inquiry previously step down.

"Both of them were eventually shown to be linked to the establishment, so they needed someone outside, and someone independent, and that's why someone came as far away as New Zealand so that you could actually break that link with the relationships that exist in England."

Advocate for those abused by the Clergy and core participant in the inquiry, Phil Johnston, said he feels betrayed, because victims and survivors need to be represented, and heard.

"When a situation's ongoing like this where people just resign when the going gets tough, or for whatever other reason, it just undermines that faith and belief in the inquiry."

The inquiry was set up in 2014 amid claims of an establishment cover-up following allegations that a pedophile ring operated in Westminster in the 1980s.

Dame Lowell's role has hit the headlines in the last few days when British media revealed she spent more 70 days of her first year in the job either outside the UK or on holiday.

The job's basic salary was around £360,000 (NZD$658,100) plus a £110,000 rental allowance and other perks.