Thanks all.
I have a regular physio i'm seeing for another injury, I'll see what/who he recommends.
I have tried to isolate the hand as much as possible with a wrist brace, but it's eye-opening just how much that little muscle does in everyday tasks that you take for granted. Little tasks like gripping a door handle or picking something up.
Interestingly, when I manipulate the muscle trigger point, the pain refers around the palm of my hand and into the pinky. I often have trouble with numbness there during riding. In April, I did the HoE300 and forgot my gloves, so rode bare handed. I had pins and needles in my right pinky for a day or two. I reckon i may have inflicted some nerve damage.
Looks like i'm taking up running for a while.