Is it in a pot or in the ground?

I keep it in a pot in the greenhouse in winter but we'll protected and in the ground in summer.I had 2 flowers on my new Brugmansia plants, just 18inch high but nothing on the little tree.

A couple of years ago, whilst visiting my local garden centre I met a Brugmansia specialist and he was telling me that the secret of prolific flowering was to use lots of potassium. He was buying Chempak High Potassium feed. He grew them in pots with a saucer beneath so as not to waste the feed. So, perhaps feed tomato fertiliser or sulphate of potash fortnightly until the end of September and then again in the spring next year.

It's probably over pruning; regular hard pruning can result in lack of flowers. The pruning rule is to cut back to within 1 inch of old wood, and although they can be kept at a height of 4-6 feet, the spread should be more than what I'm seeing on your plant, even if the spread is restricted to what's at the top of the trunk or main stem. Difficult if you're having to heavily restrict it in order to house it back under cover for winter...

Many Thanks for your tips, I think the excess pruning at the end of each season and the feeding are two big possibilities.
Thanks Bamboo and Jimmytheone