Mealy bug ?

Squash one - mealy bugs bleed red. (In fact they used to be used to make food colourings, and yes that's true...)
I use meths on a small infestation but it would take some patience to paint all those.

Mealy bug or woolly aphid, my guess is mealy bug. Aside from that, this must be the fourth member within three weeks to present this particular problem on their trees, apple, cherry..etc. Seems that this specific infestation is coming on with increasing frequency.

True. I only ever used to see them on cacti and never outdoors.

Not mealy bug. This is one of the scale insects. Used to be called American blight (no idea why.)
Soap based insecticide is the way to go, plus a scrubbing brush and repeat applications will be needed.

Looks like woolly aphid to me, provado make a treatment for it, but it has to be the ready to spray variety, which can be used on edible plants, otherwise, Bayer Sprayday.

A mealy bug is an unarmored scale insect the family Pseudococcidea. Its armored cousin for example is the San Jose Scale (USA) which is much more difficult to control. Unarmored scale insects as well as aphids can be effectively controlled with topical agent. For the armored scales systemic agents are the way to go.

Mealy bugs do not survive outside in the UK.

That used to be true, Owdboggy, but there are 4 plants which can suffer mealybug outdoors - Phormium, Ceanothus, Redcurrant and Laburnum

Must be in a lot warmer parts of the country than here then.

Ah of course, yes, that's a good point. I've only ever seen Phormium mealybug, never come across it on Ceanothus nor Laburnum myself.

Thanks for your replies. I have yet to go out and squash them to see if it is a mealy bug. Thanks for your treatment advice.