Baby carrier buggy

[angeldraws]

I am looking for a specific baby carrier/sling type thing which hooks on to straps you wear and the sling thing can then be transferred to a telescopic type frame/chassis thing.....i saw someone on the tube in London, with one and it was fantastic - it folded up tiny so the parent could just walk on the tube with the baby around her front and the buggy frame in her hand - no bulk or awkward space-taking equipment - anyone know of such a thing?

i tried to catch up with the parent when she got off the tube to find out where she got it but i lost her....tch!!