Absences from the UK Letter

[bradlinntu]

Hi all,

Could somebody help me out here? I'm on a Tier 2 visa and about to change my employer (in January). I'm now preparing a letter stating my absence from the UK during my current employment and going to have my line manager to sign this.

I wonder that can I do this letter while I'm still employed by my current employer (a university based in London) because my line manager will also leave this university at the same time (but to a different university than my next one)? So in this case I won't be able to have his letter after December.

Thanks in advance.