Tier 2 Change of Employers - travelling

[d7689]

Hi,

I will get a new Tier 2 visa due to changing employer but the start date of the new CoS/Visa is mid January 2017 when I start my new job. My visa with my current employer should expire in March 2018 supposedly. I have got some questions:

1) I will continue to work with my current employer until the start date of the new CoS in mid January. I assume this is allowed, correct?
2) If I travel out of the UK and return on 2 January, will I be denied for entry to the UK? For some reason I thought my current visa will become invalid after the new visa is issued, as my sponsor will have been changed. Therefore I will not be able to enter the UK until the start of the new CoS in mid January if I leave now. Any thoughts?

Many thanks for your help in advance. Best regards