You can go back 4 years, you have to keep records for 6 years but revenue can go back forever. You will not only owe the tax but the interest and penalties. By the way how did this come to light.
Insufficient information provided for a meaningful reply. Receiving 50K (£ or € ? ) is only part of the equation.You need to be more specific as to the asset disposed of & the amounts involved.
CGT is based on
{ [Net proceeds of sale less indexed (to 2002) cost ] - Personal exemption } x rate of CGT in force . Interest at Revenue rates prevailing is then added. Penalties depend on how this has come about. Unprompted disclosure gets a lesser penalty than if Revenue have to chase it.
thanks for your answer graham it was in pounds and it will be an unprompted disclosure which will be a help as revenue are only just questioning me not chasing it up yet.