Actually, I think there is a considerable market that rail could capture. Esentially the mixed load freight forwarders business.
A huge amount of freight traffic consists of less than container/wagon load. Anything between individual parcels to multiple pallet loads. These are typically picked up and shipped within the UK by the various competing logistics businesses in a hub and spoke operation. So a small partial load is collected by a truck on a local pick up route, taken to a local depot where it is then sorted and reloaded onto a larger truck to be forwarded to another hub. There it can be loaded onto a third truck for local delivery, or in some instances forwarded again to another more distant hub before being transferred to a local delivery route for the final drop off. Most of the trunking is done by HGV or airfreight, depending on distance/value (and weight sometimes).
Thats where rail could take some of that business, in the intermediate stages. If they could create a network of rail/road interchange hubs, the local pickup could still be done by trucks for door to door delivery. The bulk intermediate flows however, could be shipped by rail from hub to hub. This should, in theory be competitive on time and cost as this would not add extra transhipment time to the process (since you are just replacing truck to truck transfers with truck to rail transfers).
On the rail side you would need a network of hubs at major interchange points. These would essentially be large warehouses with a siding loop or two running through with platforms at deck height so palletised goods can simply be wheeled off quickly and transferred to the waiting trucks.
The goods trains would be either conventional curtain sided rail wagons loco hauled, or (my pet theory) converted curtain sided pacers for smaller loads, - a freight MPU. These would run to a timetabled service, and a single train could service multiple depots in sequence, loading and unloading as required.
This could be competitive on time/cost especially for the +24 hour medium/long distance traffic. Plus there would be clear environmental benefits from fewer trucks, less CO2 etc. Road would still perform local delivery, and air would still take the fast high value freight, but there is a lot of valuable business in between that rail could and should be carrying.
The biggest obstacles of course, are the huge costs to setup and the large question mark over network rails reliability. But I think it would be worth pursuing, perhaps by starting with a trial (two rail hubs).