Any MPs back in parliament early to bone up for the coming terror debates should swing by the exhibition in Westminster Hall. It marks the 400th anniversary of the Gunpowder Plot and recalls another era when governments thought it necessary to confront not just acts of terror but also the religious ideology that might spawn them.
The Prime Minister believes it is no longer enough to punish those who directly organise terrorist acts. He also believes action must be taken against ideas and words that might lead indirectly to violence. In the half-century leading up to the Gunpowder Plot the English Crown took the same view. Where in the reign of Elizabeth II the ideological enemy is seen as a perverted interpretation of Islam, in Elizabeth I's time it was Roman Catholicism.
As today, the majority of the "suspect" population in 16th-century England- the Roman Catholics - insisted they were loyal to the Crown. But, again as today, there were real examples of sedition - such as the Babington Plot to put the Catholic Mary Queen of Scots on the throne - which kept suspicion alive. As today, there was a backdrop of international religious conflict. Protestants and Catholics were tearing continental Europe apart in a war which, even by the standards of the age, was remarkable for its brutality.
The combination of overseas threat and conspiracy at home convinced the government then - as now - that it was no longer safe to wait for the threats to materialise in deadly form. Instead, the whole motivating religious philosophy had to be confronted. In the shadow of the Spanish Armada, the rules of the game changed.
When Elizabeth I ascended the throne, the Act of Supremacy made the link between suspect religious observance and treason. Enforcing the break with Rome, the ministers of the new queen laid down that "no foreign prince, person, prelate, state or potentate, spiritual or temporal . . . shall use or exercise any manner of power or privilege, spiritual or ecclesiastical, within this realm". Those who still believed their first loyalty was to the Pope invited charges of treason. Mohammad Sidique Khan, as shown in his pre-suicide video, clearly also believed his first loyalty was to a transnational religious community and not to the state of which he was a citizen.
Now the British government intends to ban extremist literature and close down unacceptable Islamic websites. Elizabeth I's ministers passed laws banning Catholic literature and made it a capital crime to attempt to convert anyone to Catholicism. As with our modern campaigns against foreign "preachers of hate", there was particular suspicion
of priests entering the country. If caught, they could expect no mercy. Between 1581 and 1588, the year of the Armada, 64 priests were executed.
So did it work? England defeated foreign invasion and preserved the Protestant ascendancy. Domestic and foreign conspiracies against the realm were seen off. The price, however, was an enduring suspicion of Roman Catholicism. Even after the defeat of Bonnie Prince Charlie in 1746 removed the last chance of a Catholic seizing the throne, a further 80 years passed before king and parliament felt secure enough to allow Catholics the vote. And today, four centuries after the Gunpowder Plot, the heir to the throne still may not marry a Catholic.