The accuracy of sub-coulomb (d,p) reaction tensor analysing powers, calculated using the conventional DWBA theory, is investigated. Two outstanding uncertainties in the DWBA method, relating to a) breakup of the deuteron in the coulomb field of the target nucleus, and b) the presence of T R tensor interactions in the deuteron target system, are studied quantitatively. Particular emphasis is placed upon the reaction 208Pb (d,p) 209Pb, at Ed = 9 MeV and Ed = 7 MeV, and its applicability to the measurement of the parameter of Johnson and Santos. Coulomb break up is treated in dipole approximation using perturbation theory and an adiabatic prescription. Special attention is paid to the use of a realistic state dependent interaction in the P-wave n-p continuum. Coulomb and strong tensor T[R] terms, obtained from both elastic scattering and break up models, are discussed and are included through a generalization of the conventional, Local Energy Approximation, DWBA stripping formalism. The resulting coupled differential equations are solved numerically. Results of calculations show that both effects studied must be accounted for in any analysis of precision experimental data at 9 MeV and/ or 7 MeV. Theoretical uncertainties in the strong interaction contribution to the T R potential, to which calculations at 9 MeV are sensitive, are found to be unimportant at an energy of 7 MeV. The effects of singlet ([1]S[0]) breakup of the deuteron are also shown to be completely negligible.