Updating the deeds (i.e. the process of effecting a sale) is trivial, though if you want to count these are indeed pages of paperwork for each property. It's all that comes before that takes time: consultation on route, land purchases, compulsory purchase orders, appeals, etc.

That being said, there must be more than that because it seems to me that every infrastructure project (even without purchasing land) takes ages and costs accumulate fortune for what it is. An example is the work on existing lines and stations as part of the Elizabeth line work outside London.

This seems specific as, overall, I would say that red tape for individuals and businesses is less than in, say, France or Germany.