The position in law is thus summarised in Halsburv 's Laws of England, Hailsham edition, Vol. 22, page 112, para. 191: " Whether or not, in any given case, the relation of master and servant, exists is a question of fact; but in all cases the relation imports the existence of power in the employer not only to direct what work the servant is to do, but also the manner in which the work is to be done.": and until the position is restated as contemplated in Short vs J. & W. Henderson Ltd., (supra), we may take it as the prima facie test for determining the relationship between master and servant, 160 The principle which emerges from these authorities is that the prima facie test for the determination of the relationship between master and servant is the existence of the right in the master to supervise and control the work done by the servant not only in the matter of directing what work the servant is to do but also the manner in which he shall do his work, or to borrow the words of Lord Uthwatt at page 23 in Mersey Docks and Harbour Board vs Coggins & Griffith (Liverpool) Ltd., and Another (1), " The proper test is whether or not the hirer had authority to control the manner of execution of the act in question The nature or extent of control which is requisite to establish the relationship of employer and employee must necessarily vary from business to business and is by its very nature incapable of precise definition.