I would imagine that you have a duty to inform them of the correct details of the night's events.
What you have is a penalty notice for disorder. If you decide to pay the fine then you will not be admitting guilt and there will be no record of criminal conviction being made against you.
For sensitive job applications such as doctors, the notice may be reffered to on an Enhanced Disclosure check at the Chief of Police's discretion, based on his determination that the notice is relevent to the application.
I'm sure (it must be surely?) that the ticket is still valid, they have your address I assume and so would be able to contact you if you did not pay the fine withing 21 days. It will not be a conviction if you pay. It may be a conviction if you decide to go to court, but this seems unlikely given that they were unable to issue you with a caution due to lack of evidence, and therefore may have difficulty in proving your guilt.
Facts stated are to the best of my knowledge, im sure most of them are correct but please do not rely on them! Hope it helps.