Davey,
After such a long period the information regarding the case will be held on microfile only at Scotland Yard
The force will have no access to it and removal will be a matter for the CRB.
Discharges are a subject of great debate in that :
Are they a conviction? You were discharged from the court, therefore you were not punished and did not receive a conviction as you pled guilty?? You have a criminal record but it can be argued that you have a spent discharge not a conviction.
Al forces have different policies with regard to destruction of records - check with the force who dealt with you to thier policy.
You do not need to disclose spent offences unless applying for jobs ie: police, courts, social care, teacher etc.
I would apply for your own CRB check �10 and see what comes back - You may have a clear file anyway.
Otherwise include in your application a copy of your CRB and explain the situation.
BEST OF LUCK