The government does pardons, not the monarch

[muriel_volestrangler]

although they are "in the monarch's name". The last monarch to try a pardon on his own was George IV (reigned 1820-1830), according to Wikipedia, referencing a House of Commons note:

https://en.wikipedia.org/wiki/Royal_prerogative_of_mercy

Not since the 19th century has the monarch attempted to exercise this
prerogative personally. King George IV wished to influence the Lord
Lieutenant of Ireland in exercising the prerogative of mercy in relation to a
death sentence for an inhabitant of Clare who had burned his own house
down. When Sir Robert Peel, the then Home Secretary, threatened
resignation, the King gave way. Cases of persons sentenced to death at the
Old Bailey were once considered by the monarch at a meeting of the Privy
Council. George IV often advocated mercy until over-ruled by his advisers.

https://researchbriefings.files.parliament.uk/documents/CBP-9877/CBP-9877.pdf

And the current government, though Labour, are trying to "look tough" - there's no chance they'd let anyone off if they were convicted.