Mentioning this in case it helps anyone else.
The previous time I tried to top up the AdBlue it was disastrous. Bought a 5ltr Redex branded can of AdBlue, which comes with what they call an easy pour spout. But came to realise easy pour is not the same as no spill! Even though it had an air bleed built into it, the AdBlue just kept bubbling back out no matter how careful I tried to be, ending up all down the side of the car, which is not nice. Rapid and thorough clean up was needed.
So this time around I bought the Greenchem 4ltr starter kit, which comes with Greenchem's CAREFILL non-drip spout, and I have to say it is absolutely brilliant! Not a drop spilt!
What looks like a flexible tube is actually fairly rigid, with just enough "give" in it to avoid straining the car's filler cap, but stiff enough so can push down firmly (as you have to) to open the valve. Took less than a minute to fill, keeping if firmly pressed home all the time.
Before I started I assembled the spout to the can ensuring everything tightened, and held it upside down a few moments to check nothing leaking, before then putting it onto the car's filler point. You do need to ensure it is nice and square onto the filler, and needs a good firm push to open the valve, then keep it pushed on firmly. And do make sure the white seal is in place between the tube and the can when you screw them together.
I was expecting the worst, and waiting for AdBlue to go all over the place, but in less than a minute the glugging stopped and the 4ltr can was empty. Note the car had been telling me to fill up with a minimum 3.5ltr and maximum 4.5ltr.
Also, when you unpack the spout from its long plastic package, be careful how you open it, because it is reusable with a plastic zip at the top, so take care to not damage the zip, or inadvertently cut it right off!
I now this maybe comes across as an ad, but it's simply that I've not known how to get AdBlue into our car sensibly, and this has now sorted the problem