Well, in theory you would be breaching trust by signing an undertaking to make UK your long term home (remember doing this in you intial HSMP application) and then moving on. This might make it difficult for you to get back to UK on HSMP later etc.
In practice, I do not know of anything that can stop you from moving on from the UK - you came here, saw stuff and did not like it. It is quite as simple as that really and well within your rights.
Also, H1B visa has some requirements that you need to meet. So long as you meet those the US authorities should also not have any problems with your existing status (providing of course, that the current status is legal wherever you are!).
Having said that, I must emphasise that I am no legal expert so if you are really really worried about this, contact a legal adviser. You can ask your relatives here in the UK to get in touch with Malik Solicitors etc. I know lots of Asians use these guys.
http://www.maliklaw.com
Gut feel is - coming to UK for a short duration, esp without a confirmed job, is not the best way forward.