which size pots would be ideal for oleanders

i got mine about a week agoe and mine needed repotting so all iv done is put them into a lot bigger pots thy seam ok and happy as thy grow maybe thy will need bigger but at mo thy r fine

I got mine a couple of months ago, some went in the ground and two into raised beds. My brother bought some this time last year but unfortunately most didn't survive the frost earlier this year :(. Perhaps not as hardy as we thought.

Depending on the variety, you may eventually need huge pots, a meter or more across and deep. I would see how well they do in a 30 cm one first, before making that kind of investment--both in money and in effort!
Oleanders need special conditions to thrive in the UK.

its me again as i said i put mine into bigger pots and theres new shoots comming now ITS GREAT THY ON MY WALL AND IT GETS VERY WINDY THY SEAM OK WITH IT THOU sorry about that im writring with my head down loll

Wind in itself isn't a problem for them, but it may reduce the heat buildup that they will need for bloom. In the UK, I would suggest a southern exposure, out of the wind, if possible.