My immediate solution was simply to disconnect the fuel pump earth so I could get on with the wipers. I would return to investigate this later.....
Getting under the car with a wheel off I could see the culprit was a short length of flexible fuel hose that joined two hard lines high in the rear arch, which would get wet and drip when the line was pressurised. The problem was a jubilee clip, just out of sight, that had to be tightened.
However, as I looked further downstream I realised the offending connection was only 30cm short of a factory fuel pipe union joining two lengths of hard line. Then checking upstream, the flexible hose was fixed again to the original hardline that disappeared into the boot. In the boot it had now gained another flexible hose connecting it with the fuel regulator - but only after passing through a stepup connector to get it from 6mm to the 8mm ID demanded by the regulator outlet.
So this one metre of fuel line started with a metal union and then ran through six jubilee clips to get it only as far as the fuel regulator. A classic case of 'just one more clip' being added by multiple owners over many years. While Bo'nes was too soon to allow for any radical replumbing, I figured I could at least replace that stretch of hose with something more robust.
Having resolved to do it, I pulled its entire length between the metal union and fuel regulator. Then realised I was holding something that looked like a 3/4 scale model of a mediaeval Welsh rice flail, bristling with jubilee clips.
Working with this hose, it certainly helps to following the instructions and use a brand new 32T hacksaw blade, but I found putting it all together to be a coast. As was fitting the new JIC union to the hardline. I tied it all down and there was not a drip in sight.