Archbishop Vincent Nichols will be made a Cardinal by Pope Francis on today.
The leader of the Roman Catholic Church in England and Wales will join 18 others being elevated to the rank of cardinal in a consistory ceremony at the Vatican.
Sixteen of them are under 80 - meaning they will have the right to vote for the pope's eventual successor.
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Accompanied by the Duke of Edinburgh, the Queen will attend the opening ceremony of the fifth session in the Holyrood chamber.
Ms Leadsom has received the backing of Ian Duncan Smith, the former work and pensions secretary.
The former shadow work and pensions secretary is considered a more viable candidate than Angela Eagle, a Labour source has told ITV News.