Start work w/ student visa, leave for 1 year to train, WNxt?

Here is my case:
I started work under my UK student visa, which at that time was vaild for 3 more months or so. Right after starting work, my company sent me on a long term training program to the US (9-12 months), where I am now.

Right after I started I also applied and obtained a NI numbre and pay tax in the UK as though I was there - although I am not..

What happens upon my return? My company needs to apply for a WP on my behalf - I am told -, but in the mean time, since I am not phisically in the UK (but get monthly salary in my UK bank account there) should I pay tax at all? And is this whole thing legal? Do I need a work permit while not in the UK? - For the US I have a Business B2 visa, so do not actually work here.

Thanks!