Best process:
1. Obtain LO (With buyout condition) *MUST*
2. Resign
3. Communicate with current employer and HR on release date
4. Finalised and viola

*If future employer doesnt issue any buyout condition in LO, dont bother to resign
**If current employer doesnt allow u to leave by payment of notice in lieu, speak to HR and escalate, no employer can hold any staff from leaving in this world
***If there is no firm date, please ask future employer to issue "dummy" LO, mentioning "estimated" commencement date + buyout condition