After legal action was taken by residents along the proposed route new route through issues of planning blight, the station on the current site was constructed in 1881.
Successive years and governments brought planning blight and hopes deferred once again until the school buildings reached an advances state of dilapidation.
The think tank also said significant environmental and social costs were not included in the assessment of the economic case, with several areas likely to be affected by planning blight.
Dangers of extending the period with loss of momentum and possible planning blight have to be balanced by the risk of too rapid a transition with poor quality peparation.
