Whatever the purply/blue stuff is, it seems to have formed an intimate relationship with the white verbena. Kinda cute, really. Please tell me the name. Thank you.

Lobelia, I've got it everywhere.

There's Trailing Lobelia and Bush Lobelia which are grown as annual bedding or in planters here.

https://en.wikipedia.org/wiki/...

https://www.google.co.uk/searc...

It can set around if conditions are right and you might find some plants grow the following year but generally they are treated as annuals here.

I knew that. Once. It practically grows wild here.

This is L. erinus 'Crystal Palace', an annual that reseeds happily