Two men have been charged with using threatening, abusive or insulting words or behaviour following a "flour bomb" attack in the House of Commons.
Mr Harrison and Mr Davis appeared at a news conference on Thursday
Patrick Ronald Davis, 48, of Worthing, Sussex, and farmer Guy Richard Harrison, 36, of Ashurst, Steyning, Sussex, will appear in court next week.
Tony Blair was hit by packages of flour dyed purple while speaking at prime minister's questions in the Commons.
It has prompted an urgent review of security, led by security service MI5.
The prime minister was replying to questions from Tory leader Michael Howard on Wednesday when he was hit on his back by one of the packages thrown from a gallery above him.
MPs were evacuated from the chamber for more than an hour.
Mr Blair was replying to the Tory leader when the dust was thrown
Campaign group Fathers 4 Justice claimed responsibility.
The incident happened despite a £600,000 bullet-proof security screen being installed in the chamber at Easter.
Other new security measures costing £5m are also being introduced, including a new entrance to the Palace of Westminster.
On Thursday, Leader of the House of Commons Peter Hain said recommendations from the security services would be considered next week and "some hard lessons" needed to be learnt from the flour bomb attack.
But he insisted: "We need to strike a proper balance between proper security and the rights of public access to Parliament and its members."
Mr Hain said there had been "a very old-fashioned culture around the House of Commons for far too long, not just from many of the authorities involved, but also from MPs".
Home Secretary David Blunkett said the security services would bring forward recommendations "very quickly indeed", but it could mean there would be more restrictions on the public areas of the House of Commons, he said.
Labour peer Baroness Golding said the two accused were guests of hers and she offered "unreserved apologies" to Commons Speaker Michael Martin, MPs and fellow peers.
She said the men had got tickets to the Commons at a charity auction.
At a press conference on Thursday, Mr Harrison was asked what his reaction was to the possibility that public visitors could be permanently banned from the Commons.
He replied: "I hope we have increased the security for the government."
Mr Davis and Mr Harrison were charged under Section 5 of the Public Order Act 1986. The pair were bailed to appear at Bow Street Magistrates' Court in London on Wednesday, 26 May.