Really Non-stretch Fishing line - Authoraitative advice please

I am a lawn bowls umpire and we are told to use fishing line for certain
measuring between bowls to find which is closest to the target. Sometimes
over a distance of as much as 10 or 15 metres the difference between 2 bowls
is very close, say only 10 millimetres or less, so for accurate measurement
it is essential to have a line which does not stretch.

I went to a local shop (Watford, UK) and was sold "Dacron braided leader"
which was said to be non-stretch but in practice I have found this is far
from the case. So I am seeking really authoritative advice on what line to
buy as a replacement.

I need a minimum of about 45 metres in length (because on occasion we also
use a line pulled tight from one end of the bowls rink to the other end),
and I believe price is not really an issue - I don't want to spend more than
is necessary but would not jib at £25 if that is what it takes to get
something which really offers the minimum stretch. I need the full
identifying name so as not to get the wrong product.

If you cannot yourself advise, do you know a chap who can !!!
Thanks so much
--
Regards, Jack Sadie