1) As per extant instructions as contained in Para 244 of Indian Railway Establishment Code (IREC), Volume-I, Fifth Edition-1985, Third Reprint Edition-2008 reads with Para 1401 of Indian Railway Establishment Manual (IREM), Volume-I(Revised Edition-1989), First Reprint Edition-2009, permission to a Railway servant to submit an application in response to advertised post outside the Railways like to Departments outside the Government of India or under a State Government, shall not ordinarily be refused unless the head of the office or the department in which he is employed considers that the grant of permission would not be consistent with the interest of the public service . The competent authority should interpret the term “public interest” strictly subject to the condition that forwarding of application should be the rule rather than the exception. The cadre controlling authorities would consider each case from the point of view whether the Railway servant could be spared or not, no other general condition should be applied in taking a decision in the case.
2) in your case NOC has been refused by railways
3) further you did not disclose in your application form while applying for police post that you are employed by railways
4) you may resign from Railways but they railways may refuse to accept your resignation . disciplinary action can be taken against you for applying for police job without NOC
5) it is in your interest to continue with your present job