Yes, there are many unsung British engineers/scientists during that period including:
Oliver Heaviside - Wikipedia, the free encyclopedia (who I consider to be the best Electrical Engineer of all time)
William Huggins - Wikipedia, the free encyclopedia
Jocelyn Bell Burnell - Wikipedia, the free encyclopedia
It happens quite often, that a scientist working outside the mainstream is the ones who make the great discoveries.
Still, I would not call Colossus the most important computer of all. Because even the Babage adder can be considered an early computer...and many would argue that Von Neumann's or Hoff's are really the turning ponts that formed computing as it is today.