H1B visa stamping London

[chanduucs]

Here is my case:

I stayed in US for 3 year 9 months on H1B with company X.
I have an approved I 140 with company X.
Travelled to India and got a 221g followed by a rejection in Mar 2011.

Working for an MNC in INDIA. Now in UK for an onsite from May 2012.

Have an extension H1B approval from company Y now.

Can I attend for visa stamping in US Embassy, London... I will be staying here until October end(6months TIER 2 ICT visa UK).

Can someone help me on this?