When you are Self Employed your pay tax in advance in January and July, but Companies pay tax 9 months after their financial year end.
So if you formed a Company and it started trading in April 2011, its year would end 31st March 2012 and Corporation Tax would be due in December 2012.
As a director of your own company you will be paid as an employee (PAYE) and get paid dividends as a Shareholder. Dividends are paid out of taxed profits.
What this means is that a Director taking a minimal salary, will probably have a tax break of 12 plus 9 = 21 Months.
In addition the company will buy the assets of the sole trader and it may be possible to include a value for goodwill.