It spreads rapidly through its seeds.

Thank you Cammomile.

Yup it is

Definitely!!!!!

Not so much by increasing clump size but agree it seeds all over the place. Easy to pull out though.

In my old garden it spread a lot and I couldn't get rid of it, but in this garden it hardly spreads at all ...

I, too, had it in my old garden and, like Hywel, I couldn't get rid of it. I know it's very pretty but I won't have it in this tiny garden.

Oh thank you all so much, I will give it a miss and try and find something less invasive.

In my experience most ground cover plants are invasive, hence the name ground cover. I like Sempervivum, the Houseleek. It flowers and has pretty succulent rosettes of leaves. Doesn't invade either but spreads gently.
There's also the low Campanula which has delightful rich blue bell shaped flowers most of the summer. It does like the sun though.

Thank you Arbuthnot,It is for a shady border,I will be very careful what I buy,I do not want it to get out of hand.

I agree with the comments. The roots are so easy to pull without disturbing plants around. I find that if you think it is attractive in your garden you should try it. It is not exactly thought of as a ground cover...

If you would be satisfied with shiny green leaves most of the year and dainty flowers in spring look at Epimediums. They clump up slowly but not invasively and some varieties have beautiful spring foliage.

They sound very nice,thank you Steragram, I will have a look.