Hi Nats
and, Longer Iron - your behaviour is shameful, you lost an entire mile of motoring over a distance of 120 miles - such waste!! But, those are really good figures! You can get 60 mpg if you try
Sadly this car will never do 60 mpg...it is a very early C3 picasso - the slightly later cars had the engine/fcu tweaked for better mpg but I think even they would struggle to get 60 just because of the shape LOL
I had a Volvo in my mis-spent youth. Most comfortable car ever - a 244GL and you know what? They all do 25 miles to the gallon.
When I had my own glider - my towcar was a volvo 264 - with the Peugeot 2.7 litre V6 and auto box...it was such a torquey engine that the gear shifts were ultra smooth....great towcar (22mpg LOL).
I replaced it with a 244 (28mpg summer/25mpg winter) and I loved the footwell kick open vent - great for hot summer days

My worst ever towcar was a ford escort 1.6 diesel...no power but 65mpg easy to achieve
I found the cause of the increse in fuel consumption.
There is a rubber pipe leading from the injector - I assume it is a scavanger or overflow pipe from the injector to the . . . fuel tank . . ?
Yes it will be the return pipe,quite a normal fault on older diesels...well done on your fix btw