If you acquired assets on or after 20 September 1985 and did not keep records, or your records have inadvertently been destroyed, you can still do something about it.
If you bought real estate, your solicitor or real estate agent may have copies of most of the records you need. You should be able to get copies if you ask for them.
If you made improvements to an investment property, for example, if you built an extension, then ask for a copy of the builder's receipt for payment.
If you bought shares in a company or units in a unit trust, your stockbroker or investment adviser may be able to give you the information you need.
If you received an asset as a gift and you did not get a market valuation at the time, a professional valuer can tell you what its market value was at the relevant date.
The main thing is to get as many details as possible so you can reconstruct your records. Make sure you keep sufficient records in the future.