Many businesses will structure their affairs by using a group of companies. There will be a parent or holding company at the top, and this will hold 1 or more trading subsidiaries.
Advantages of using a holding company
There is no tax on dividends from subsidiaries to the holding company, so you could build up funds to invest without suffering additional tax.
The holding company could sell shares without suffering tax if eligible for substantial shareholdings exemption (eg hold >10% of a trading company for at least 12 months).
In my experience, a key reason for using holding companies is to enable losses and assets to be transferred around the group to minimise corporation tax or capital gains. You could also use the holding company to charge “know how” or management fees to the subsidiaries, which could save tax if the holding company is registered in a lower tax jurisdiction (& managed and controlled offshore).
The major downside to using a holding company is that it may create “associates” for tax purposes which means that the corporation tax limits get split by the number of companies in a group. Although, when the full rate comes down to 20% in 2015 this won’t make any difference.