Do you think subterranean city's would impact less on wiled life and green areas?

In england and the rest of Britain our city's are very over crowded and we are running out of building space . Anyway i saw an advert the other day about a city under the sea and it got me thinking if they can do it under the sea why cant they build under ground city's do you think it could work and if not why not . I think it would open up a lot of space but yes it would be a massive amount of upheaval constructing the new city's maybe im just dreaming but i think it would be a good idea