‘Just because you have not been sent a notification to complete a tax return does not automatically mean you are not liable to complete one. Now is the time to consider your affairs and take action where necessary,’ says Lagerberg.

Anyone who has realised capital gains – or losses – on shares or other assets needs to complete a tax return. It is particularly important to do so in the case of losses, as these can be carried forward to be used against gains in future years.

Many investors have lost significant sums as a consequence of companies either ceasing to trade or shares becoming worthless; for example, Northern Rock and Bradford & Bingley. Before these losses can be offset against gains, it is necessary to make a ‘Negligible Value Claim’ to HMRC.

In addition, the credit crunch created a surge in company mergers, rights issues and takeovers, And investors – or their advisers – now have the onerous task of working out what this means in terms of CGT liabilities.

This can be very tricky. What you may consider to be a loss could in fact be a gain, according to HMRC’s complicated share identification rules. Be aware, too, that you are now required to supply the taxman with a copy of all underlying calculations used to work out capital gains or losses. You can get help from http://www.timetotrade.eu/cgt_uk.php.

Timetotrade’s Capital Gains Tax calculator helps investors calculate their capital gains on shares, unit trusts and OEIC transactions, in advance of the 31 October 2009 tax return deadline.

To generate the calculation, you simply input acquisition prices of shares or funds, and timetotrade works out the rest. This includes complex calculations for Section 104 holdings, equalisation payments, notional distributions, share reorganisations (such as mergers, rights issues and takeovers) and share identification rules (for those who know what these are). The tool can also be used to calculate indexation allowance and taper relief (see the HMRC’s guide here) that were applicable prior to the changes to CGT legislation in April 2008.

Dary McGovern, managing director of Sensatus, the developers behind timetotrade, says, ‘We have worked closely with private investors during the development of timetotrade. In doing so, it quickly became apparent that a solution was needed that would help investors quickly determine their tax liabilities. Using timetotrade, investors can now do this.’