Labour's former General Election co-ordinator Tom Watson has pledged to "fight very hard" to retain the party's links with trade unions after the GMB union announced it was slashing its funding.
Mr Watson, who was involved in the selection of Labour's election candidates, resigned his shadow cabinet position over the Falkirk row.
He wrote on his blog: "If this is the beginning of the end of that historic link, it is a very serious development that threatens a pillar of our democracy that has endured for over one hundred years.
"Some will scoff but they are fools to do so. That party card stands for something more than confirmation that an annual direct debit has been processed."
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Among those expected to attend the ceremony will be former US President Bill Clinton and ex-Northern Ireland first minister Peter Robinson.
Five people have been killed and 40 injured after a car and knife attack in London on Wednesday.
A wet, wintry night in places with rain and hill snow slow to move away from southern Scotland and northern England.