Case C-624/19: Judgment of the Court (Second Chamber) of 3 June 2021 (request for a preliminary ruling from the Watford Employment Tribunal — United Kingdom) — K and Others, L, M, N and Others, O, P, Q, R, S, T v Tesco Stores Ltd (Reference for a preliminary ruling — Social policy — Equal pay for male and female workers — Article 157 TFEU — Direct effect — Concept of ‘work of equal value’ — Claims seeking equal pay for work of equal value — Single source — Workers of different sex having the same employer — Different establishments — Comparison)