Mike Lyle wrote:
So how do you get them to form a hedge?

A tall hedge g But seriously, he wants 6m high and after spending the
last two weeks looking at formal and informal hedges ... I am so tired
of the usual plants given as examples. I suggested the quercus ilex
because as my cousin did it, 5 along as standards, evergreen heads
touching, which she prunes in spring. It gives a fabulous tall hedge,
with bear trunks up to 1.5m. I have also seen them pruned with a square
shape but on a high trunk, not an hedge, in a park in Bordeaux. It's
lovely and really different.