Change of employer

Hello,

I started working in the UK in January 2013 on a fixed one year contract and I was issued a Tier 2 visa valid for one year. In February 2014 I was offered a continuing contract by my current employer and I applied to extend my visa on 10 January 2014. I also registered my biometrics on 19 February 2014 and currently I am waiting for my documents to be returned which could take several more weeks. In the meanwhile, I had a job offer yesterday from another company who has the license to sponsor and is willing to sponsor me under Tier 2. The new company wants me to start as soon as possible given that I have a 4 week notice period, but the problem is that I haven't received back my documents for the previous application from UKBA and I don't know whether I should submit a new application without my documents or wait until they are returned to me.I also don't know when I should resign from my current job. Any ideas?

Many thanks,

I