CanalWays

I started a reply to this, then had to go away for a few days because I started trying to respond to every misconception - and the result was a mess. Perhaps the best place to start is by making a very simple point. The present canal system is designed for boats up to about 30t displacement carrying, for the sake of argument, maximum loads of around 25t. At 4mph (the point at which bank erosion starts with current technology), you will be getting possibly 4mpg under ideal conditions. So to equal one 44t Artic doing 56mph, in terms of ton miles, you will need roughly 25 boats, and you will use maybe 40 times the fuel. Inconveniently, the main proposals for barge traffic are inside congested cities where artic speeds are extremely low. Widening isn't an option there, but often there are rivers (rather than canals) which can be used.
The barges on European canals range from around 360t to 4000t. At these sizes, there starts to be some economic point. However, to make use of them you would need to rebuild the entire system, confiscating in the process all the houses and businesses along the banks to gain the necessary width - say 40M, plus large amounts of land for large automated locks, catch ponds, weirs and access. And the carrying capacity will still be far less than a motorway of the same width, and it will be less fuel efficient because, as should be obvious, water has more resistance to movement than tarmac and pneumatic tyres. It was this lack of efficiency that caused canals to be obsoleted for freight by railways.
I could get very political about the way your scheme seeks to confiscate land and assets from people outside London for the benefit of people in London, just as supermarkets (based in the South-East) seek to impoverish farmers elsewhere in the country. It is not clear why people in the North should have their water stolen to send to the south, merely for the convenience of people who choose to live there. But something tells me you are a Londoner, and Londoners are remarkably obtuse about the irrationality their belief that they own everything. I know - I am a renegade Londoner who moved West thirty years ago.
However, in fact you would find the resistance to this confiscation came in many shapes and forms. Quite a lot of people do not want this country entirely converted into Watford. Towns like Hungerford and Newbury might express a little concern about the destruction if their town centres and transport links. The environment lobby - who I assume you regard as a collection of weirdos - might be a little bit upset about the wholesale destruction of sites of scientific interest. And the tourist industry would be a mite peeved at losing a sizeable slice of its income.
Back to practicalities. You may not be aware that canals go up and down, which is what locks are for (and you will need pretty big locks for your 360t barges.) They are not a good way to transport water, in fact the more common issue is one of transporting water to the canal. Open stretches of water mean that getting large volumes over summits is a bit of a technical issue. And how fast will that water have to flow? You are going to need concrete lining for the entire system.
Of course, the sensible solution is to send water through pipes. This allows you to use pressure and get readonable flow rates. What's more, you could route these pipes underground on optimised routes instead of meandering all over the country. Using modern boring equipment, surface disruptions would be minimal.
You would also increase the transport capacity of the country far more, with less disruption, by adding a single lane to every motorway and dual carriageway. Now why is that not practicable?
Finally, a word about British Waterways. My only connection with them is that I pay them over £400 a year for a licence. But I actually like BW. Far from being some fuddy-duddy, stuck in the mud organisation, they are actually a very progressive, well run company with an excellent training scheme and a huge fund of knowledge about canals. You could have saved yourself a lot of trouble by talking to them, though admittedly you wouldn't have got a story in the Inq. They would have given you the technical information you so conspicuously lack, and the economic data.