Lilacs, even dwarf forms, have very extensive root systems and love to 'sucker' and produce new plants.
Use as large a pot as you can and keep it well fed and watered. Lilac is very easy. But if you can find some way to root them into the soil, that would be far preferable and will give you a much better plant.

Hi Bertiefox thanks for that,how big a pot do you think i'd need to keep it healthy, i've recently retired and I have more time to sort my garden out,(her indoors is over the moon).
The garden is not that big and we just want to use it for relaxing and the occasional barbie.There is a small lawn and 2 small patio's with a small summer house 'i've potted 4 cordylines and 5 bush roses to spread around I did'nt want to plant in the ground really because we'd like to move them occasionally,I really like dwarf lilac, but can you suggest a simular shrub with less extensive rooting that I coud put in a pot.
As you can probably tell i'm a complete novice,so I would really appreciate your thoughts.
Thank you.
Don.