Corporation tax is based on profits after directors salaries and has lower rates than personal tax.
Shareholders of Limited Companies can take money from the company in the form of dividends. These do not incur any national insurance for the shareholder or the Company.
Dividends are effectively tax free for shareholders up to the higher rate tax band and then are taxed at an effective top rate of tax of 25%.
Operating as a Limited Company gives much stronger credibility in the market place.