> Firstly, the 'bat shed' (officially SWBMS) is expected to cost £100m. This is neither expensive nor wasteful for a structure nearly 1 kilometre long and "designed to accommodate up to 36 high-speed trains passing through the structure every hour of operation for 120 years, plus frequent conventional rail traffic in addition" as reported by Architects' Journal[1].
It might be good value for a 1km tunnel (or not, I don't know) but I think this argument misses the wood for the trees.
The main point is more "should we be spending £100m on a bat tunnel?"
i.e. What else could £100m of public money buy us, and would it be better than a 1km bat shed?