Martyn 51....sounds to me like you have greenfly...I think the white bugs are adults who lay eggs which then hatch into greenfly which then secrete honeydew which is sticky. I have a plum tree which both last year & this is thick with greenfly. I have tried using neem oil, but as this is an insect repellant & the bees are currently feeding on the honeydew I apply this only to the trunk of the tree where the beasties are crawling. Damage limitation is my only mode of attack & am spraying surrounding unaffected plants with the neem. The white bits which have collected on a black chair under the tree, are I am sure the dead adults....?? die after laying eggs??? If any one has a better suggestion....can I know too please? I do not want to get rid of the tree, as where will the little b's find next year?? My roses?? I am in the next county to you!

The white bits are the exoskeletons of aphids. they shed them when they increase in size.
Bees do not eat honeydew, ants do.
Personally I leave the trees alone. Spraying with anything is so hit and miss and likely to damage friendly insects.
If you must then try using a spray of Horticultural soft soap after dusk when the bees and hoverflies have gone to bed.

Sorry to disagree but I have had aphids on my apple tree and the leaves have curled as the aphids have been injecting them. Bees have been visiting the curled leaves and I have come to the conclusion that they are there for the honeydew secretions.

Just had a good read up on Honeydew and apparently bees do eat it. Not good for them in some ways as it stops them collecting pollen and so they get a protein deficiency.
Google Honeydew Honey for a lot of info.
Other problem is that insecticide used to control the aphids collects in the honeydew and even if the bees are not sprayed directly the residue can kill them. Sad.