Just filled the 340 with fuel. On returning home find fuel dripping from under the car(car was parked with 2 wheels on the kerb). Was coming from what seems to be an overflow pipe . Anyhow I removed the leaky peice of pipework and tried to find some at the local motor factors. Nothing . All they have is standard fuel pipe which is a couple of mill smaller . Anyone know where I can get the right size?

Someone will confirm that it's 12mm ID? You might need about ¾m of it. Plenty of stuff on fleabay.

Our search says:
HERE
12mm

HTH.

It's 12mm fuel hose and it has leaked like a sieve on both my 340s. Replace it as a matter of course. Buy low pressure fuel hose (SAE 30 R6 or equivalent) as you need to be able to bend it and it get it through the gromits.

As a botch your local motor factors may have hydraulic oil hose, 1/2" SAE 100 R6 would be OK, although totally over the top. If they don't have any oil hose either then it shouldn't be hard to find radiator hose in either 12mm or 1/2". Only use radiator hose as an emergency fix because it is not specified for fuel and may go hard/brittle over time. Many motor factors will try and sell you radiator hose as fuel hose anyway, always check what the hose actually says on it, if it has nothing written on it don't buy it! As a general rule use SAE 30 R6 for general low pressure petrol use, R7 for low pressure diesel and R9 for high pressure fuel use.

Halfords always used to have it, but in the thicker fuel injection pipe. The thicker stuff lasts longer, but is much more of a PITA to fit, because as Alex says you have to bend it through the gromits.