Oh dear. Well it'll have to take its chances, but it is true that, in the UK, these are usually only temporary summer visitors if you cannot give them a greenhouse or conservatory over winter, and you're in a pretty cold part of the country.

If you can manage to grow from seed or take a few cuttings and keep those indoors, then you can still have one (or more) next year - instructions on how to propagate here, though its aimed at people in warmer climates, but the basic information is the same, just that you need to keep them inside during the winter till frosts are over

https://www.gardeningknowhow.com/ornamental/vines/mandevilla/mandevilla-propagation.htm

Hi, I was buying plants this afternoon, and saw some for sale, there was no mention of the fact that they're not hardy, they were very nice plants, but I managed to resist the temptation to buy any of these. Derek.

Hi Bamboo

Well that will teach me to impulse buy without having a clue what conditions the plant will require...
I'm going to try and see if I can take it back because it was a bit steep for an annual.

Hi Derek

After buying, I looked at various sites and they without exception said; plant in a container and then bring inside before any sign of frosts. I don't have that option at all unless it would survive in our garage.....
That will be why I haven't seen them in many gardens round here!

Thank you both for your help.
HollyDuff

That's a useful lesson - when you do see a plant you've not seen before, especially during summer, think twice, ask questions - if the staff can't give a clear answer, don't buy. Unless you have a smartphone, in which case, google the name and check it out...

Not a chance. I'm a zone 6 USA and I have had them blooming right into late October but they succumb to Jack Frost. They do work hard at producing flowers late spring, summer and fall so you do get your money's worth. The trouble with bringing outdoor plants into the home (not garage) is that more likely than not you will bring in a few ant colonies and centepedes into the home too. Finally, Mandavilla love to have their roots pot bound so if you get another next season keep it in the pot just put a pinch of fertilizer into the watering can.