Usually, if you lose money investing in stocks and shares, you can offset it against gains you make on other holdings. This applies across assets. So you could offset stocks and shares losses against a gain made on a buy-to-let property, for example.
However, it only applies where the gain is taxable in the first place. Assets held in ISAs and private pensions are not subject to capital gains tax and therefore losses can’t be offset against anything else. So, Carillion shares – for example - held in a simple online dealing account could be offset against gains on any profit-making shares you sell. Those held inside your ISA or your SIPP can’t.