Unusual nesting place

I was at a garden centre yesterday with my Mum and discovered that a bird had made a nest in a 6ft high climbing Clematis. It was a small nippy little brown thing so I suspect that it was a wren. Basically I saw the bird zip into the plant, zip out again shortly followed by a fecal sac. As we walked about the little bird did a very close fly-past and quite made me jump :)
I told an employee who said that they do get that fairly regularly.

Could be a wren.though thay usually nest near the ground . I kept getting almost zapped by pigeons today , their wings were missing the side of my head by and inch or so.