Stephen Hawking, et al., write a letter to The Telegraph urging the UK to forgive Alan Turing's conviction

Turing statue by Stephen Kettle at
Bletchley Park, commissioned by the
American philanthropist Sidney Frank
(Source: Wikipedia)

Alan Turing, a renowned British mathematician who improved and automated the Polish crack of Nazi message encrypting machines and is credited by many for paving the way for Allied Victory, was arrested for "Gross Indecency" with a 19-year-old — Arnold Murray — after Turing went to the police following a series of petty thefts in which Murray and a confederate were involved.
     Turing underwent "chemical castration" (estrogen injections) for a year, after which he died from cyanide poisoning, either as a suicide from a suspected tainted apple he ate (never tested) or from inadvertently from experiments he was conducting.
     Not everyone agrees with Hawking. Martin Robbins, in a blog hosted by the Manchester Guardian wrote:

...I'm not sure that the British government have earned the right to pardon Alan Turing. Not as long as the attitudes that led to his persecution are still very much with us, and entrenched in that very same government.The language of Hawking et al's letter is remarkably clumsy; its plea that the government should 'forgive' Turing carelessly implying that he did something to be forgiven for.

John Graham-Cuming, who was behing a 2009 campaign resulting in a government apology to Turing, is against a pardon:

...Secondly, even if a pardon is appropriate, a pardon for simply Turing would be unjust to the other gay men who suffered under the law. There were many, many others. And there are men alive today living in Britain with a criminal record because of offenses committed during the time the laws were in force. I could get behind a petition for a pardon for all those people, especially since living people are still hurt by that law, but not just for Turing. Pardoning him doesn't help the living.       But even that's unnecessary. Subsequent to the 2009 apology campaign the UK government introduced legislation that actually does roll back the criminal convictions of gay men. The Protection of Freedoms bill has already passed all stages in the House of Commons, two readings in the House of Lords and enters (this coming Monday) committee stage. That means it's close to being law.

Here is the Hawking letter:

SIR – We write in support of a posthumous pardon for Alan Turing, one of the most brilliant mathematicians of the modern era. He lead the team of Enigma codebreakers at Bletchley Park, which most historians agree shortened the Second World War. Yet successive governments seem incapable of forgiving his conviction for the then crime of being a homosexual, which led to his suicide, aged 41.
     We urge the Prime Minister formally to forgive this British hero, to whom we owe so much as a nation, and whose pioneering contribution to computer sciences remains relevant even today. To those who seek to block attempts to secure a pardon with the argument that this would set a precedent, we would answer that Turing’s achievements are sui generis. It is time his reputation was unblemished.
Lord Currie of Marylebone
Lord Grade of Yarmouth
Lord Faulkner or Worcester
Lord Rees of Ludlow
Astronomer Royal
Lord Sharkey
Lord Smith of Finsbury
Baroness Trumpington
Sir Timothy Gowers
Rouse Ball Professor of Mathematics, Cambridge University
Dr Douglas Gurr
Chairman, Science Museum Group
Professor Stephen Hawking
Sir Paul Nurse
President, the Royal Society