Open Question: National Insurance Number's question,please?

Good afternoon,I left the UK a few month ago,I took my NI contributions and I filled a few papers at the HMR saying that I was leaving the country for good,so I attached my P45 to claim the money and I stopped to work in the UK and so my NI. Things now are different than I thought,so I would like to go back to the UK! Am I going to have problems by asking for another one?Am I allowed to go