"The ceremony, marking the 400-year anniversary of the plot, will see the Duke of Northumberland shaking hands with the Marquess of Salisbury"
"February 1605 was the final month in which the plotters were trying to dig a tunnel under the Houses of Parliament as part of their scheme.
In March the gang discovered that the cellar underneath Parliament, where Guy Fawkes, was eventually arrested was available to rent.

so its celebrating the 400th anniversary of the plotters realising they didn't have to dig tunnels.

phooey any kid can tell you that the anniversary of the plot should be celebrated on november the 5th.
Not because of the plot
but because it failed