Today Jeremy Corbyn issued this statement:
The whole of the Labour Party and Labour family — and indeed the whole country — will be in shock at the horrific murder of Jo Cox yesterday.
Today, I have travelled to Birstall to bring the condolences of the Labour movement to Jo's family and constituents.
Jo Cox was an outstanding and inspiring new Member of Parliament, who had already shown in her life and work her dedication to the cause of peace and social justice.
She was killed doing the job she was elected to do — representing the people she was elected to serve, doing her duty to the public and our democracy.
We have requested, and been granted, the recall of Parliament on Monday. The gravity of what has happened means that I have decided, in consultation with our Deputy Leader Tom Watson, and our General Secretary Iain McNicol, to suspend Labour's national referendum campaign this weekend. I have also asked that local campaigning is suspended until Sunday.
The killing of Jo Cox was not only the tragic loss of a fantastic human being, woman, mother, wife, friend and comrade to so many of us inside and outside Parliament: it was an assault on democracy itself. It was an attack on the right of everyone to have their say in how our country is run and for those that the people elect to be able to listen to and represent them, without fear or favour.
As Jo's husband Brendan said in his extraordinary and poignant tribute, Jo Cox was also the victim of hatred and intolerance.
Ours is a country where tolerance and respect for other people and different viewpoints have always been highly valued.
Jo Cox stood for tolerance, justice, peace and human rights. We must come together as a country and face down hatred and intolerance in our society.
We send Jo's family, her two young children and her husband Brendan our deepest condolences and love. They are in the hearts of all of us.
Today we have established an online book of condolences so that Labour members and supporters can send their own messages of condolence and express their thoughts at this troubling time. I hope this will help us all to come together in solidarity and in dedication to a better world.
You can add your message here: http://www.labour.org.uk/jo-cox
Finally I want to pay tribute to the extraordinary work of Labour Party staff and members at all levels and in all parts of the country who worked yesterday to deal with this horrific situation. Their commitment in such circumstances is an inspiration to us all.