No, no, no. Your manager doesn't get to 'accept' your resignation!
"It is a common misconception that an employee’s notice of resignation is not valid unless it has been "accepted" by the employer.
The position at common law is that a notice, once validly given, is effective and can neither be "refused" by the employer or "withdrawn" by the employee, without the other's agreement.
Generally, unless the employee’s contract of employment stipulates that resignation has to be in writing, there is no requirement for a notice of resignation to be in a particular form and you cannot insist that notice is given in writing before it will take effect. It is enough for an employee to tell you that he is resigning, provided his statement is clear and unambiguous.
Difficulties can arise, if an employee tells you that he is resigning in the heat of an argument, and it is not clear whether he actually means it or is just “sounding off”. If this occurs, you should give the employee the opportunity to withdraw his resignation once he has cooled down. It is good practice to put this in writing, so that you can evidence the fact that you did give the employee time to reconsider, in the event of a later dispute.
Once an employee has resigned, both parties should know when the employment relationship will come to an end. Employees are required to give at least the amount of notice set out in their contract of employment. This is subject to a statutory requirement to give ‘at least’ one week’s notice after the employee has worked for a month or more. So if the contract states that the employee has to give two weeks’ notice, that is all he is required to give, even if he has worked for you for a number of years and you consider him to be a “key” member of staff.
It is important to remember that employers are also required to give their staff statutory minimum periods of notice which increase according to the number of years worked and are subject to a maximum of 12 weeks’ notice where the employee has worked for 12 years or more. As a result, employers and employees do not necessarily have to give the same amount of notice to one another and an employee is only required to give the same amount of notice as his employer would to terminate his employment, if this what his contract stipulates.
Employees’ sometimes give their employers no notice, or a shorter period of notice than that set out in their contract of employment. An employee is only entitled to do this if he is resigning in response to a fundamental breach of his employment terms (constructive dismissal). Therefore in normal circumstances, if you are not willing to accept shorter notice, write to the employee and remind him that he is required to work throughout his contractual period of notice. If he refuses to do so, you only have to pay him up to the date he actually stops working.
Once you have received notice of resignation, it is good practice to acknowledge this in writing and explain to the employee when his employment will end and to make arrangements for payment of final salary, outstanding holiday and the return of any company equipment etc. If your employee is subject to contractual restrictions (known as restrictive covenants) it can also be helpful to remind him of these." Irwin Mitchell