Formal proof is a notion developed in the early part of the 20th century by logicians such as Bertrand Russell and Gottlob Frege, along with mathematicians such as David Hilbert (who can fairly be described as the father of modern mathematics) and Nicolas Bourbaki, the pseudonym of a group of French mathematicians who sought to place all of mathematics on a rigorous footing.
The report said that for more selective universities, such as those in the Russell Group who tend to ask for higher A-level grades, mathematics requirements can be a useful filtering tool.