I think that of the many misunderstood plants in the garden, ivy has to rank pretty well at the top of the list. There can be no doubt that if it’s allowed to run rampant, it can wreak havoc. However, understanding a little more about the plant might help you to feel differently about it.
Look closely and you will see that although the variegation colours are roughly the same, the shape of the leaves, comparing the upper stem from the lower one, are quite different
The top stem with its definite three-points to its leaf margin, this is juvenile growth. This is the form that will grow quite quickly and when it has found a solid service (this is something that it senses) it will attach itself with adventitious roots that quite literally stick to the wall/fence/whatever.
It is this juvenile growth that causes most of the ‘I hate ivy’ emotions in the garden.
The lower stem in the pic is adult, and you can see that the colours are the same, but the leaf shape is quite different. Gone are the three distinct points, to be replaced by a much smoother and more graceful leaf margin.
Now, I cannot tell you exactly when an ivy plant decides that it is time to grow up, all I can tell you is that it does and the growth habit and leaf shape are quite different. It is this adult form that will produce flowers and berries, and is generally much better behaved. If you were to cut back an adult stem, there is absolute no danger of the plant reverting back to being a teenager.
Understanding this, you are now well equipped to keep a screen of ivy looking good and providing much needed early nectar and berries for the birds and insects in your garden.