The Official Secrets Act must be signed by you and pertains to 'official secrets' you may become party to as a servant of the Crown. It is not illegal to share this as a common civilian. Whether it is safe to do so is another matter entirely.
http://researchbriefings.parliament.uk/ResearchBriefing/Summ...
edit: beat to it by a minute!
That said, and IANAL, this document is not covered because of 5(2) - there's no reasonable grounds for believing that releasing this document is damaging to national security. It's a draft, so does not describe any measures currently in effect, and the draft will be made public in a few days when it is submitted to parliament, before it has any effect.
That's not true. It's a law not a contract; everybody is bound by it: http://researchbriefings.parliament.uk/ResearchBriefing/Summ...
>Do you have to sign the Official Secrets Act to be bound by it?
>It is not necessary for a person to have signed the Official Secrets Act in order to be bound by it.