The bit that says
"Who can manage a joint account
When two or more people decide to open a joint bank account, they have to sign a form called a mandate. The mandate sets out what the joint account holders can do, for example, who can sign cheques and take money out.
You can cancel the mandate at any time without the agreement of the others. You would need to do this, for example, if you want to change the terms of the joint account or close it.
However, it is possible to draw up a mandate which only allows you to change the terms of the joint account or to close it with the agreement of all the account holders."
But it also says in another place
"If there is disagreement about a joint account
If you have a disagreement with another joint account holder, you should cancel the joint account mandate straight away.
If the mandate isn't cancelled straight away, any one account holder will still be able to get access to the account and the bank won't be able to refuse to pay them.
When you cancel a joint account mandate, the account will be frozen. All the account holders will then have to agree on how to divide the money up between them. If it's not possible to agree, the courts will have to decide how to divide the money up."