Raising roof on Victorian terrace?

[dewl]

I was always under the impression that it was a definite no-go but saw this pic on Rightmove.
I have a loft room with velux windows but the ceiling height is only 5'10" at the peak. I know lowering the ceilings on the first floor is an option but I had a builder round who said this would only give me another few inches.
Is raising the roof a viable option?

Forgot to add the pic

I would imagine the cost would be prohibitive unless you live in a very high value area. And how much roof clearance could you actually gain without spoiling the front of your house?

Sorry, not very helpful!

Check the planning history for that house, they probably got permission to raise it to the chimney height but no higher so it didn't spoil the street scene too much.