A payment to someone on taking up employment may be compensation for the surrender of a personal asset or the loss of a valuable right unconnected with their employment. If it is, it will not be a profit from the employment. It will arise from something else.
If the sum received is capital and derives from an asset it may be taxable under the capital gains tax legislation (see CG12940).
In Hose v Warwick (27TC459) a lump sum paid to an employee on becoming a director of the company he worked for was held to be compensation for the transfer to the company of the valuable business connections he had built up for himself. It was not taxable as earnings within Section 62.