OMG it sounds just like a weed which has invaded my garden! I haven't a clue what it is, but believe me, it's a right pain. It will climb anything, and I've just had to have tons of it removed from my roof, where it reached after almost choking a large grevillea to death! Roundup kills it, and I suspect it's an offering from overhead birds, otherwise it appears from nowhere, but will take hold in the tiniest crevice. It has a small flower which is almost black in colour.

Julie, I have no idea what this plant is or whether you and daisy are talking about the same thing, but I would guess that if it has trifolate juvenile leaves it is a legume of some sort which may be a place to start to get a decent i.d.
Daisy were the flowers on yours a pea-like flower or something different? Julie, has your plant flowered yet and if so is it similar to Daisy's?

mudlark

Mine has not flowered yet. When I asked the nursery who supplied it by email, what they had growing near their Lady's mantle and explained the situation, they replied that they had experimented with a herb in that patch the year before but he couldn't remember what it was. It has popped up in three of the seven plants I got. Have it in pots in a hot house.

Thankyou Daisy and Mudlark, The legume comment gave me a starting point. Looked up Isabell Shipard Book and it does look like her photo but shall wait for a flower to see if it is Butterfly Pea, foliage looks very like it. Thanks again.

I could be seedling passionflowers.. The wild passionfruit which doesn't have fruit you can really eat. Very pretty, but very invasive. There are quite a few species that occur as weeds on the east coast.