The message
from Mike contains these words:

The trouble is this...

The problem patch is under my patio slabs and grows up inbetween them
making access to the roots rather difficult. The bits in the lawn and
in the borders I can live with! I'm only planning on pouring the SC
down the gaps between the slabs, keeping my distance from the lawn of
course.

Not a snowball's chance in Hell.

Glyphosate, following the roughing-up instructions is the only way,
unless you want to poison all the soil in the area (not just beneath the
slabs) with something like sodium chlorate.

You never know where it will leach to, and it is unlikely to penetrate
to the deepest roots. The *ONLY* way is with repeated applications of a
systemic weedkiller. And even that is pretty useless in the long term if
you can't attack it on your neighbours' plots.....

--
Rusty
Open the creaking gate to make a horrid.squeak, then lower the foobar.
http://www.users.zetnet.co.uk/hi-fi/