Keeping my Olive tree small

I have a good problem: my Olive tree is too happy!
I planted it in the polytunnel, thinking it would like the climate better in there than outside, but it is hitting the roof! There is very little soil depth where it is (maybe 18 inches) but it can go sideways I guess. I`ve had it about three years now, and only watered a little in it`s first year. It flowered well in the first year, but didn`t set fruit, and both summers since then it has put on more vegetative growth with very few flowers, no fruit. I have been nipping the tips off the shoots, and it is very bushy, and seems to grow almost year round with no additional protection.
My question is can I prune it to keep it small where it is, or is there another method of keeping it small? If I do prune it how best for fruit production? I think I have managed to germinate a couple of olive seeds because I suspect it needed a pollinator. Am I going to struggle here to keep it small enough for the tunnel?
Thanks for any advice.

Hi, Nancy

From what I understand, yes, you can prune the top branches.

Here is a Guide to Trimming Olive Tress that might help, especially about your question on fruit production:

https://www.gardeningknowhow.com/edible/fruits/olive/pruning-olive-trees.htm

Have you thought about using your trimmings to make more trees? Here is a thread that might help:

https://permies.com/t/70661/making-olive-trees

Best wishes for many olives and olive trees!

Hi Anne,
Thanks for the links. It looks like I can cut back the tree quite hard in early summer, so I`ll give that a go. I`m just really surprised how vigorous the growth has been, not what I expected at all!
Several of the links mention uses for Olive leaves, I`m wondering whether to try them as a tea - I`ll have plenty after pruning next year! They may be anti inflammatory and anti viral as well as reducing blood sugars...seems like a miracle cure all! see webmd for example.
I don`t really need to propagate this tree. I`m pretty sure that the trees wouldn`t like it outside, although they might survive if I can find a well drained spot. I`m hoping I can get a few seedlings to survive and flower to pollinate this first tree (the seeds were much cheaper than another tree.). Mind you, friends and relatives further south might like a potted olive tree as a gift.

Nancy said, "Mind you, friends and relatives further south might like a potted olive tree as a gift.

This sounds like a great idea.

I don't have an olive tree though Olive tea sounds good and with bemefits.  

Depending on the variety, olive trees have both female and male flowers and self-pollinate. If you are not getting olives in a tree that size, (and it is obviously quite healthy) it may be a non-bearing olive tree. Or, it has enough sunlight to grow but not to produce. It naturally grows in the hot, dry Mediterranean, after all. Like untreated olives, the leaves would be extremely bitter for a tea. Cutting branches make for gorgeous, fresh indoor arrangements, or for gifts. with or without mixing flowers in.  If you just like its foliage in your greenhouse, you can trim it down quite dramatically and let it grow back annually. The trunk will just start getting bigger. Should you get it to fruit, you will need to preserve them as they are also extremely bitter.

When we lived in California, we had 3 acres of Italian varieties: Frantoio, Lecino, Mandolino, and Pendolino. The parent trees came from Italy where the olive oil from this varietal mix was a gold winner. Each year we picked tons of olives and had them milled into gallons and gallons of our own olive oil. The best advice we received from the tree seller was, while you technically don't need a varietal mix, the amount of fruit produced is much higher than with just one variety.

Thanks for your first hand insight Molly.  I'm pretty sure that the olive I bought was Leccino from Lubera, which should be good for oil according to Lubera.  I'm aware I'm pushing the boundaries slightly by growing olives on Skye, but I can grow early grapes pretty well under cover here. It is pretty warm in summer at least in the tunnel, it may be that the growth is not matured though. We get very long daylight hours, but without much intensity in the light so lots of soft green growth, which maybe does not promote flowering. I am getting a few flowers so I really think a pollinating partner will help in getting fruit (hence the seedlings). I didn't think about this when I bought the one plant originally.
I didn't really expect the olive to like it so much - I had one in a pot that came with the house. I never watered it and it died (in a rather prolonged way which I won't go into here). That one never flowered and never put on much growth poor thing. The soil in the tunnel is not as acidic as most  of my land. Part of it is where former buildings stood, so there is probably lime from lime mortar, and limewash in it.  But I need to get a feel for how to prune the tree sympathetically to contain it in the tunnel, since there will definately not be a chance of fruit outside here.

Yay for you for being able to grow olives and grapes! What an accomplishment. You do know you will need LOTS of olives to make oil, right? (and an olive press and the rest of the equipment). That's a beautiful tree in the photo. Olive trees are quite picky so you are doing an amazing job.