But spread over many constituencies it would have no effect. See comments about the first past the post/ safe seats above.
There are several considerations at play here which may not be obvious to overseas commentators:
Cameron is trying to appeal to the "Daily Mail" readership who make up a large chunk of his support. The DM is a newspaper in the loosest sense of the world which has one aim - to make its readership scared/angry. It does this by targeting foreigners, the EU, the BBC, Muslims, the gay community, the Labour party, any number of materials that cause cancer (though some can miraculously cure it as well - e.g. coffee - the DM relies on its readers having a short attention span/memory) and anyone who doesn't fawn over royalty**. One of its current campaigns is against porn.
He's also reacting against the atrocity in Tunisia. "Something needs to be done!" "I'll do something -- sorted!!"
The UK government in general, irrespective of party, has a terrible reputation with regard to implementing IT systems. Their incompetence is one of our safeguards.
Finally this is the summer - the "silly season" when there's little news.
** How do you confuse a Daily Mail reader? Tell them that gypsies kill paedophiles.