1 Prof. Jones: Since this is the Siege Perilous, it implies the Round Table must also be in Tintagel Castle.
2 Monty: Unless it was taken somewhere else by later raiders.
3 Prof. Jones: Who would be so uncouth as to take an English table without all of the matching chairs?
4 Minnesota Jones: The Welsh?

The English and the Welsh have a long history of mutual hostilities. So much so that Wikipedia has a page containing a List of Anglo-Welsh wars. Fortunately they seem to have stopped in the 15th century.