It depends on what you do. If you are a consultant who is employed by one company only (ie a contractor) then there is no tax break as HMRC considers you as taxable at PAYE levels as you are effectively a full time employee. If you mean that you will go around working for several companies offering consultative support then the best option is to set up a limited company and pay company tax on your companies earnings, pay yourself a dividend on you profits and then pay much lower income tax on the remainder. With a limited company you also have the option of writing off many things as an expense (cost of computers, part of rent/mortgage paid if your offices at home).
The key though is to have multiple clients not just one key one, the hmrc will look for that as the number of 'consultants' who are basically employees of companies who have been made redundant and reemployed in their old roles as contractors has rocketed in recent years.
Big bit of advice is to get an accountant. It will cost up to a grand a year but will save you three times that and he will advise you of all the advantages.