The writer seems not to understand how most entrepreneurs and growing businesses operate as he concludes his letter:
British job creators must be allowed to keep more of what they earn so they can hire more staff, purchase more equipment and reinvest in their businesses. The chancellor must take heed by removing the 50p income tax rate.Most 'British job creators' run companies that pay corporation tax on their profits. The main rate of Corporation Tax is not 50%. It's just 28%. Only monies paid out of the companies to the owners and directors are subject to 50% INCOME tax (on amounts above £150k pa).
Together with National Insurance, the 50p tax rate means that the highest earners keep less than half what they earn. This cannot be ideal but there do seem to be political reasons to keep the 50% rate for the moment.