The UK must reconsider its relations with Saudi Arabia if the state ordered the murder of a journalist, a senior MP said.

Commons Foreign Affairs Committee chairman Tom Tugendhat said the UK should work with its allies on its response following claims Jamal Khashoggi was killed while visiting the Saudi consulate in Istanbul.

Mr Tugendhat said it was important to establish the facts, but if the Riyadh government had murdered Mr Khashoggi then there could be a downgrading of diplomatic relations and a boycott by UK ministers.

In a sign of the international concern, UN Secretary General Antonio Guterres said he wanted to know the truth about what happened and expressed fears such disappearances would happen more regularly and become a “new normal”.

People hold posters outside the Embassy of Saudi Arabia in the US with photos of missing Jamal Khashoggi. Credit: PA/AP

Riyadh faces a chorus of international calls to shed light on what happened to the Washington Post columnist, and business leaders have already shunned the regime.

Financial Times editor Lionel Barber announced the newspaper would be pulling out of its partnership in a high-profile economic conference in Riyadh, while Sir Richard Branson has frozen several business links with the Gulf state.

Tom Tugendhat said Saudi Arabia could not be treated as a ‘normal state’ if it is responsible for the death of Jamal Khashoggi. Credit: PA

Mr Tugendhat said International Trade Secretary Liam Fox should boycott the Future Investment Initiative in Riyadh later this month if Saudi involvement in Mr Khashoggi’s disappearance was proved.

“The first thing for us to do is for us to get together with our allies, the United States, the Europeans and others, to discuss very seriously what’s going on,” Mr Tugendhat told BBC Radio 4’s Today.

“The idea that we can treat Saudi as a normal state if it practices state-sponsored murder outside its borders is simply not true.”

He added: “We may be talking about downgrading diplomatic relations, we may be talking about restricting support for certain areas”.

A security guard looks out of the entrance of Saudi Arabia’s consulate in Istanbul. Credit: PA

Mr Guterres told the BBC at the International Monetary Fund meeting in Bali: “We need to have a strong request for the truth to be clear.

“We need to know exactly what has happened and we need to know exactly who is responsible and, of course, when we see the multiplication of this kind of situation I think we need to find ways in which accountability is also demanded.”

Former foreign secretary Sir Malcolm Rifkind called for Britain to impose sanctions against Saudi Arabia following the disappearance of a Saudi journalist.

He told BBC’s Newsnight: “If the current Crown Prince remains in power for the indefinite future, then in the first instance the United Kingdom must work with the United States, France and other countries to see if there can be a combined response, a punishment of some kind, of sanctions of some kind.

“If the United States was not willing to take part then the United Kingdom has to consider action that it will take in its own name.”

Former foreign secretary Sir Malcolm Rifkind called for Britain to impose sanctions against Saudi Arabia. Credit: Isabel Infantes/PA

A critic of Saudi Arabia’s de facto ruler Crown Prince Mohammed bin Salman, Mr Khashoggi was living in self-imposed exile in the US and writing opinion pieces for the Washington Post before he vanished.

He visited the consulate last Tuesday to obtain a document confirming he had divorced his ex-wife, in order to allow him to remarry.

Turkish officials have said he was killed on the premises and his body removed.

Saudi officials have denied the allegations as baseless.