A week or so ago I ordered a Split Ring Compression Fitting spanner like
this from Toolstation: http://tinyurl.com/y9wa57q

MWH asked for a report when I got it.

Bottom line is that it has much thicker ring walls than I expected and
therefore not as useful as anticipated.

Having said that nice bit of kit and no regrets. Having a "proper" plumbing
spanner certainly is less hassle than continuously adjusting an adjustable.