It turns out that I do have an SWR meter suitable in a Zetagi meter that I bought for HF, I checked the specs, and it's good for up to 200 Mhz !
In the shack I use a colinear antenna for 2m, this is up in the loft, the shack being in the front upstairs box room, so I tuned around to find activity on the Plymouth 2m repeater, around 30 miles away, signals were coming in around an S5.
I plugged in the moxon and could receive the same signals around an S7, turning the antenna made a noticeable difference, as did turning it horizontal, it was fun making the signal come and go at will, having only ever used dipoles and verticals.
Upon checking the SWR, I got the following readings -
144000 - 1.6
145000 - 1.5
146000 - 1.9
This was with the antenna hanging vertically from the top of the shack door !
I did some extra checks and have concluded that the antenna has a bandwidth for a 2.0:1 SWR of about 5Mhz !