Having read the comments on here I tried a couple of things which have made a bit of difference.
Firstly, I tried Beejay2112's suggestion of pressing the perineum and found that does indeed make the urine flow again. Needs a few presses sometimes to fully empty but definitely short cut time-wise.
The other thing I found was that, when this happens, if I force myself to hold on, the urge to release more urine goes away temporarily. About 10 minutes later I have a strong urge to go again and when I do go, all the remaining urine comes out in one go.
So, two possible methods that may help others suffering from the same problem.