I have never seen Big Ben
The new Denison watch, apparently is made by the makers of Big Ben which as we all know was Whitechapel Bell Foundry.
Yes, Big Ben is a bell, not a clock, so to answer my title question - it was certainly not Dent of London Ltd.
This watch bears the name Denison who was one of the designers of the clock in the Clock Tower at the Palace of Westminster. I have tended to refer to the tower as St. Stephen's Tower following a tradition established by Victorian journalists..
However in June this year 331 MPs voted to change its official name from The Clock Tower to Elizabeth Tower in commemoration of the Queen's diamond anniversary. This seems appropriate as the tower at the other end of the palace is Victoria Tower.
I hope Dent of London apply more precision to making watches than they do to creating advertising copy.