Theresa May has insisted the UK must do “everything it can” to press Brazilian authorities to uncover the truth about the disappearance of British journalist Dom Phillips and indigenous expert Bruno Pereira.

The Conservative former prime minister made the plea to Boris Johnson in the House of Commons after police arrested a second suspect in connection with the case.

Police said the suspect, Oseney da Costa de Oliveira, 41, is the brother of the first suspect.

Amarildo da Costa de Oliveira, 41, also known as Pelado, has been named as a suspect in the disappearance but arrested for allegedly carrying a firearm without a permit, a common practice in the region.

He is thought to have been among a group of men who threatened the missing pair near an indigenous territory on June 4.

It comes after police said personal items belonging to the two missing men were discovered in a river on Sunday.

In a statement, they said objects recovered included a backpack and a pair of boots belonging to Mr Phillips, as well as a health card, black trousers, a black sandal and a pair of boots belonging to Mr Pereira.

Mr Phillips, 57, and Brazilian indigenous expert Mr Pereira, 41, vanished from a remote part of the Amazon last week and are believed to have last been seen early on June 5 in the Sao Rafael community.

Speaking at Prime Minister’s Questions, Maidenhead MP Mrs May said: “My constituent Dominique Davis is the niece of Dom Phillips, the British journalist missing in Brazil, alongside the indigenous expert Bruno Pereira.

“Will my right honourable friend ensure that the Government makes this case a diplomatic priority, and that it works to do everything it can to ensure that the Brazilian authorities put the resources necessary to uncover the truth and find out what has happened to Dom and Bruno?”

Prime Minister Mr Johnson replied: “FCDO officials are working closely now with the Brazilian authorities following his disappearance on June 5.

“The minister responsible has raised the issue repeatedly, the search and rescue efforts, with Brazil’s justice and public security minister and what we told the Brazilians is we stand ready to provide all the support that they may need.”

Earlier, the Brazilian ambassador to the UK apologised to Mr Phillips’ family after they were incorrectly told his body had been found.

According to The Guardian, the family received a call from an aide to the ambassador early on Monday saying their bodies had been discovered tied to trees in the rainforest.

However, Mr Phillips’ brother-in-law, Paul Sherwood, confirmed to the PA news agency on Tuesday that ambassador Fred Arruda had written to the family to say the statement was incorrect.

Mr Arruda said: “We are deeply sorry the embassy passed on to the family yesterday information that did not prove correct.”

He went on to say the embassy had been “misled” by information it had received from “investigating officials”.

Mr Arruda insisted: “The search operation will go on, with no efforts being spared.”

He added: “Our thoughts remain with Dom, Bruno, yourselves and the other members of both families.”

On Saturday, separate reports emerged that police had discovered human matter in the Itaquai River, near Atalaia do Norte’s port.

Authorities previously said blood found on Pelado’s boat had been sent for analysis.

A GoFundMe set up by friends of the men neared 37,000 dollars (£30,732) early on Wednesday morning.