The Mi5 poster has every right to post, but to bring you uptodate,
here is a brief resume of this usenet legend:
His name is Mike Corley. He is part of usenet history.
He also was a champion tap-dancer in 1962/63 and 1966.

Mike lives in Clapham, South London, he first began his postings
to usenet, BBS, and online forums back in 1996, which is long before
most of you, especially google gropers, learned of he internet let
alone knew how to use it.
But Mikes paranoia of alleged MI5 persecution can be traced back
as far 1990, when newspaper editors, TV newsdesks, magazine
reviewers, radio shows et al, first received Mike's reports of his
harassment by UK security services and MI5 operatives.

Mike has his own website:
http://www.five.org.uk/

There have been numerous newspaper articles and online thesis
about Mike's postings, this is a BBC article on the subject:
http://www.bbc.co.uk/dna/h2g2/alabaster/A164404

And amongst many other covers of the Mike Corley phenomenon
there has been a modern opera about this usenet legend:
http://www.thecorleyconspiracy.com/

What the current flood is all about is hinted at in the X-posts.
He percieves uk.misc to be an MI5 infiltrated group.
And Mike is flooding it. But also it is included in the X-posts because
he knows many always respond to his posts, and you in turn flood
the group uk.misc.