How do I retrieve information about a historic Capital Loss

Back in 1989 or 1990 I made quite a significant capital loss which was reported to HMRC at the time. I've had a few changes of accountants since then and this brought forward loss is not showing on my return and I can't remember when it last did. I've now made a capital gain and wish to offset it. Is there anyway details of this historic loss can be retrieved from HMRC. I'm doing the CGT reporting myself as I'm long retired and no longer have an accountant.

Hi,
You will need to contact us direct on Self Assessment: general enquiries so that we can access your record.
Thank you.

I did that and after waiting on the telephone for nearly 1 hour I was told the records did not go back that far!

Hi,
If there is no note on your record of the loss then we are unable to assist.
Thank you.