The UK Parliament is in fact about to pass the Protection of Freedoms Bill
which will allow people to have convictions for consensual gay sex "disregarded" and erased from the records. It doesn't automatically
reverse all convictions, presumably because some of them were for non-consensual sex or sex with under-16s.
I have seen it argued that a pardon for Turing alone would be unfair because it ignores all the other people who were similarly unjustly convicted.