Buddleja x davidii Buzz Ivory.

google white dwarf buddleia and you get lots of suggestions. but check the variety in, say, the RHS website to check its credentials.

if you decide to buy on line check the pot size they come in. some show substantial plants in the image but you get a 9cm pot [4"] with a twig in it.

Thanks to both of you for your suggestions. Much appreciated.
Marjorie