Relatives of those killed in the Manchester Arena attack have called for greater “openness and transparency” from authorities about the extradition of the bomber’s brother from Libya.

Barristers for the bereaved families issued a plea for more information about the criminal investigation and expressed their “concern and distress” at the delays to the start of the inquest.

A pre-inquest hearing on Thursday was told that oral evidence will not begin until April 2020 at the earliest, almost three years after 22 people were killed at an Ariana Grande concert on 22 May 2017.

Pete Weatherby QC, representing two of the families, told the hearing in Manchester: “We are concerned it has taken us so long to get to the point that we are at the moment. We do raise a concern that it will be almost three years since the outrage before this process actually starts.”

Paul Greaney QC, counsel to the inquest, told the hearing that the coroner, Sir John Saunders, could not begin hearing oral evidence until criminal proceedings had concluded.

The criminal prosecution is being delayed by efforts to extradite Hashem Abedi, the younger brother of the bomber Salman Abedi, from Libya where he is reportedly being held by a militia group. If he is returned to the UK he will face trial for 22 counts of murder, one of attempted murder and another of conspiracy to cause an explosion.

Weatherby expressed concern that the families were not being kept updated by police and prosecutors about the status of the extradition. “All I’m asking is that 20 months on after the outrage of the bombing families be provided with a greater level of factual data about the process,” he said. “We know that the extradition request was made in November 2017.

“What we ask through you to the CPS and police is a plea for a greater amount of factual transparency.”

Weatherby said families wanted to know “where are the proceedings up to, what has been achieved so far and what hurdles do there remain in the process of the extradition”.

“Where is Hashem Abedi?” he asked. “Because of course, given the situation in Libya, that is a matter of concern to the families. Is he in detention and is he in the detention of the UN-backed government in Tripoli or some other force?”

Weatherby added: “This is a call for some openness and transparency about where we have reached. The importance of the extradition is obvious.”

Outside court, Stephen Howe, the husband of victim Alison Howe, criticised the lack of information being given to the families and said he did not believe Abedi would ever be extradited.

“I feel as upset today as I did the day it happened,” Howe said. “There was no update whatsoever today. I walked out of court. They did not give us any answers to any of our questions. There is no point sitting there listening to nothing.”

He added: “It is very frustrating and very upsetting. I do not think they are getting anywhere with it. I am sure everyone is feeling frustrated and angry.”

John Cooper QC, representing 10 of the families, endorsed Weatherby’s request for more information from the authorities.

He asked that the coroner be given unredacted copies of any classified government documents that might assist the inquest, such as information about the role of intelligence services in monitoring Abedi.

Cooper said the families wished to explore “not so much what information they [the security services] knew about the bomber but what they did once they had it”.

Greaney, for the coroner, read an update provided last week by Greater Manchester police and the Crown Prosecution Service which said only that the extradition process was “in progress”.

The update said that more than 100 police and prosecution staff were working on data to form part of the inquest, and that more than 300 statements had been taken since the previous pre-inquest hearing in October.

Jeremy Johnson QC, representing Greater Manchester police, said he would follow up the family’s request with the force and the CPS.

He said a “comprehensive plan” was in place once Abedi returns to the UK and that he would make arrangements to update the families either individually or as a group.

Cooper, for the families, said grieving relatives were also distressed by the appearance of the spot at Manchester Arena where Abedi detonated his bomb.

He said the location of the blast was “awfully delineated” so that it was obvious where the attack happened “each and every time you go in”.

“We have raised this with the arena but not sure we have got anywhere,” he said. “We want it to be properly repaired so that tragic spot is not constantly delineated every time people walk in there.”