Why a road / rail facility and not just keep it as per rail freight, in 25 years the per rail business has not materialised possibly due t the lack of investment in rail / road freight transfer facilities elsewhere in the UK▸ , and our loading gauge does not allow for piggy back (road trailer on rail waggon)
An investment loading gauge improvements would make subsequent electrification schemes cheaper.
"Just a dream", I fear ... but I can see freight traffic coming through the tunnel, on the purpose built line from the tunnel to London, then linking to the other new line currently under construction from London via Birmingham to various points in the North. Containers on or off truck loading in Paris, Brussels and Hamburg ... coming off the train for local distribution from Birmingham, Kegworth, Barnsley and Manchester
The problem here is that most intra-European freight transport uses semi-trailers or, at the most, swap bodies. Containers are almost exclusively used for deep-sea transport as they are designed to be stacked some 10 high on the big container ships. This increases their tare weight so making them less efficient for simple road or rail transport where they are not stacked.
The cost of operating transfer stations and the delay in the transit they would cause makes it very difficult to justify their use. A two hour delay in movement would see a lorry 100 miles nearer its destination - it may well have arrived at its destination before a similar container has even left the depot. And there will be two such transfers on each journey. This is quite apart from the need to identify and build suitable transfer sites - the land requirements will be quite large which in itself is not eco-friendly.
In spite of considerable work by various parties on the continent such road-rail-road transfer only occurs in a very few cases - mainly for trans-Alpine transits where special considerations apply. Even with the German government tipping the playing field towards the railways by banning all heavy goods traffic from the Autobahnen on Sundays[1] nobody has yet found a more efficient way[2] to ship goods than by HGV.
Much as I would like to see more freight traffic on the railways one has to appreciate that the current arrangements for moving freight have evolved over many years and adequately meet the requirements of the parties involved - which include the end consumer. Any changes which come about through carbon taxes and similar will be evolutionary - not revolutionary.
[1] With the exception of perishables but including all international transit traffic.
[2] 'Efficient' is a figure of merit for a combination of speed, reliability, flexibility, ability to make very quick changes in originating and end points as well as routing, reduction in pilfering, financing costs of goods in transit, and so on.