Oleanders like heat and plenty of sun, and obviously, this year in the UK we've not had much of that apart from a week or so back in July. Clearly, yours is getting ready to flower - if the weather gets colder, or you live north of Watford, the buds may just abort, but if the weather cheers up and temperatures aren't bad, and your plant is in full sun in a sheltered spot, the flowers may yet open. Needs protection in winter if you're in a cold region of the country.

Thankyou Bamboo for your advice. I live in the north of England and so that would seem to be the reason although I was told that the plant was hardy enough to survive. I will take your advice and protect during winter.

I'm in West London and I planted one of these in a front garden about 7 years ago - its still there, and I have to keep hacking it back, its got so large, sailed through the bad winter of 2010 too - but, it is a built up area, a small front garden (so protected by the house wall, and the low wall its planted in front of, the added warmth of street paving and tarmac) and south facing, so in the right conditions, they will survive. If you've got it in a sheltered (out of cold winds) south facing spot, it might be just fine...