The message
from Adrian contains these words:

The other thing that may be worthwhile is to fit an automatic
changeover valve and two cylinders. This means that you get an
nearly-instant changeover when one cylinder empties - but the downside
is that you may not notice you've emptied the cylinder until the
second one runs dry..... In any case - we've always found that the
47kg cylinders we used for gas hob and oven lasted ages - typically
18months - so using just the one cylinder may not be a big problem for
you.

You could try the halfway approach by having 2 bottles on a suitably
valved manifold. It won't stop the problem of the gas running out
halfway through the Sunday roast but if you buy a new cylinder when one
runs out the discomfort will be shortlived.

--
Roger Chapman