Normally, you would be entitled to full pay up to the effective date of termination of employment (your last day of employment), including any holiday pay for holiday you have built up but not taken, overtime, bonuses and commission earned up to that date. Your (including holiday pay) will be subject to tax and national insurance as normal and paid through PAYE.
The law on carrying forward holiday has changed temporarily in an important way as a result of the coronavirus pandemic. If you missed out on taking your holiday in the correct holiday year because of the pandemic, you must be allowed to carry forward up to four weeks of that holiday into the next two holiday years. And if you are made redundant without having used up this holiday, the employer must pay you for it.
In addition, to holiday pay, you should get a redundancy payment, if your job is made redundant and if you qualify for payment (e.g. you have enough service - a minimum of two years is required). Redundancy pay is free of tax up to a limit of £30,000.
Deductions from a final payment may be made where there has been an overpayment, for example of holiday entitlement, but only if your contract permits this (clearly and in writing).
If you are on sick leave, then even if you are not receiving full pay, you will be entitled to full pay during any statutory notice period.
The position is different if you are on sick leave and your contract entitles you to notice that is a week (or longer) than your statutory minimum entitlement. Here, if you are off sick during your notice period, your employer only has to pay your contractual entitlement to sick pay during your notice period. This might be statutory sick pay or, if you’ve already used up your statutory sick pay entitlement, nothing at all.