Small to medium sized, semi-double, bell-shaped flowers, purplish blue on the inside, outside violet shading to pastel blue at the tips. Seedheads persistent.

To précis the story set out in the International Clematis Register and Checklist 2002 Fifth Supplement (which is available on-line as a pdf if you want to read the entire saga):

In 1959 Jackman changed the name of his selection macropetala 'Lagoon' to macropetala 'Maidwell Hall' (this name was chosen because an "identical mutation" of macropetala was found by Oliver Wyatt at his school, Maidwell Hall, in Northampton). The original name 'Lagoon' was transferred by Jackman to another of his selections from macropetala [see macropetala 'Lagoon' (of Jackman)]. The cultivar name 'Maidwell Hall' was given to Jackman's selection, not to the clone that originated at Maidwell Hall. Wyatt's cultivar is apparently still in cultivation and, to avoid confusion(!), is to be known as macropetala 'Maidwell Hall' (of Wyatt).