Hi, When discussing earthing systems using 15mm pipe a friend said that
they connected a garden hose to the end of the pipe and ran water
through whilst pushing the pipe in. I believe they got further than a meter.

Clive,

that's the way I got my 2.5m steel pipes into the ground. I works fine as long as you don't hit rocks.

But beware of a "China syndrome" :

After "flushing" the pipe into the ground it is best to secure the pipe for some days/weeks as the pipe will keep sinking even after you stop flowing water.

I found out after I got the first 2.5m pipe into the ground, leaving the end about 10 cm above the ground. I went to the water tap to close the water flow and by the time I returned to the pipe is had disapeared. Luckily the water hose was still connected to the pipe, so I could pull it up. The pipe had sunk about 30cm in less than a minute ! 

73, Rik  ON7YD