If your employer makes a payment in lieu of (i.e. instead of) your notice, rather than requiring you to work it, this payment should be based on your contractual rate of pay. What is included in the payment will depend on your contract of employment. A payment in lieu of notice would not normally include overtime payments, shift premiums and other bonuses that depend on you working.
The period of paid notice you are entitled to will be your statutory period of notice or the period of notice set out in your contract, whichever is the longer. If you are on reduced pay because you are absent due to sickness, where the employer gives you statutory notice, you are entitled to full pay while working out your notice.