Tier 2 20 hour per week before receiving curtailment letter

[alithamir1985]

Hi
I am a Doctor and I work in one of the NHS Hospitals
I am currently on Tier 2 visa general
I have resigned from my job and I will leave the Uk within few weeks
My sponsor (Hospital) will notify UKBA on 20/12/2015 to cancel my sponsorship
I have not received curtailment letter yet
My question is
Between 20/12/2015(last day of my sponsorship) and till I receive the curtailment letter ,can I work for my previous employer or other employers(Hospitals) and is this limited to 20 hours per week ?

My previous employer would not mind me working for them ,I will be paid on hourly basis as a Locum ,the term they use is Inhouse bank.
Thanks