Self-driving electric lorries would sharply reduce the cost of shipping by reducing fuel cost (my 12 gallon, 300-mile tank would cost $1.92 to fill if it were a Tesla electric Model S) and eliminating the wages of the truck driver for the 5000-mile, multi-day, cross-country journey.
Here is a simpler idea using existing technology: freight trains. You still need trucks (eh, lorries) for local delivery, but even if they have a driver they can be electric. It's also quite different than your 5000 mi example. For anything over about 200 mi, intermodal (train/truck) uses less energy and is generally cheaper. I don't know about the UK, but what the US needs is more intermodal facilities and better coordination. Even still it's more widely used in the US than many people realize. Trains can be electric of course, but even if you don't want to pay to electrify long distance lines, trains use about 1/3 the amount of diesel fuel that trucks do per ton-mile.