I am not sure that it is right (even if beloved of politicians) to say that the taxpayer has 'saved' money - it has simply spent it. 'Saved' implies getting what you originally wanted but for lower cost.
In the case of the canal network, the fundamental issue, as with rather a lot else, is the absence of a basic principle on which to make decisions - does the public want a viable network and on what basis? (ie for boats, walkers, fisherfolk, neighbours with a view) If so, at what price does support change to not support? As is the fashion at the moment, reducing spend whilst alleging waste seems to be acceptable - no mention of the waste associate with ventures such as PPI! Perhaps MP's should be paid on a performance basis . . . with OBR assessing the degree of success of each promise. One of my long term grips is that so many projects (public or private) are justified on a cost saving or cost benefit basis. But when the next idea comes along, well before the predecessor has paid back its cost with savings or benefits, that 'loss' is ignored.