Got the two cooler pipes out on Friday where they attach to the block.
On measuring the O/D of the male connection that screws into the block, it came out as 17.90 mm on my metric micrometer, which was nothing like any of the BSP, NPT sizes which I was expecting. My mechanic suggested I take the connections to Pirtek in Basildon, to see if they could make up a short bypass pipe to screw into the block mountings. They identified the thread as a metric one (M18 x 1.5) and once they'd done that they made up a flexi hose to connect the two unions together. I was concerned that a bit a rubber hose bent 180 degrees might be susceptible to collapsing internally, but they supplied a hose rated to 20 bar, which feels really solid. Also the total height of the by pass is 130mm,, well within the 190mm clearance from the block face where the bypass mounts, to an adjacent bit of chassis leg.
A very elegant solution and for less than £30.
The two guys in the shop were great and said they are often being asked to make up oil and power steering pipes/hoses for old (and not so old) cars which the car makers no longer support. So well worth a visit. Obviously take your old pipes with you. Pirtek have branches all round the country (and the world) and I'm not getting paid commission!!!