Why did the British government consider control of Egypt critical to the
British Empire?

It meant control of valuable historical landmarks. It meant control of the Suez Canal in order to have quicker access to colonies in the empire. It meant control of vital oil and coal resources for the ships of the British navy.

in his book, the riddle of the rosetta stone, james giblin talks about how there was a young british polymath and physician named thomas young who made a lot of advances on the deciphering of the rosetta stone. he says that even though young made a lot of mistakes because he was working under false assumptions, he also made huge contributions like deciphering three out of the seven symbols (more than anyone else before him). young published his findings and continued his good work but he wasn't able to progress much further due to some unfavorable situations, he still laid the basis for many other scholars and of course for the man who has been generally known to have deciphered it, jean-françois champollion