Switching sponsors

[Jvisser2485]

I’m a veterinary surgeon currently on a tier 2 sponsorship . I’ve been in the uk for 3.5 years and need another 1.5 years before applying for indefinite leave to remain . My residence permit was stolen 2 months ago after which I applied for a replacement and submitted my biometrics 3 weeks ago but haven’t received it back . I’ve had 2 seperate sponsors since moving over. I would like to move back to my original company and they are willing to sponsor me again .
They have already started with the the labour market test process and said they can issue an unrestricted certificate of sponsorship in 6 weeks , 2 weeks after the labour market test has finished .

I would like to know when it would be safe to give my notice at my current employer to gaurantee I won’t have problems ? My notice period is 3 months . Can I do it after getting my replacement brp or new cos or only when the new visa comes through ?
Just to be clear my question is when exactly can I safely resign from my current employer as my notice period is 3 months . I need to be able to tell my new employer what my start date will be and what date to put on the certificate of sponsorship As a start date .?

If I wait to get a new visa that will likely only be 2-3 months from now so should I put my start date 5 months from now to factor in my notice or 3 months from now ? .