Yes, should flower this year. Likes heat and sun - I do grow a species Canna, but its not this one, and it flowers much better in a hotter, sunnier year. In a bad year, no flowers at all.

Thanks for that. The main reason I posted the question was because they are hardly growing this year, compared to my usual experience with other cannas. But like the UK we are having the worst June in our memory/experience over ten years! It's probably going to be pushing it for flowers if the weather doesn't improve.
Hope those 80 mph winds and three months of rain in 24 hours haven't materialised in the UK, if the forecasts we hear are correct!

Don't think we've had that much rain overnight here in west London, but its certainly really, really windy... wrecking the clems on the balcony, poor things.