The Sex Discrimination Act 1975 (c. 65) was an Act of the Parliament of the United Kingdom which protected men and women from discriminationon the grounds of sex or marital status. The Act concerned employment, training, education, harassment, the provision of goods and services, and the disposal of premises. The Gender Recognition Act 2004 and The Sex Discrimination Act 1975 (Amendment) Regulations 2008 amended parts of this Act to apply to transsexual people. Other amendments were introduced by the Sex Discrimination Act 1986, the Employment Act 1989, the Equality Act 2006, and other legislation such as rulings by the European Court of Justice.
The Act did not apply in Northern Ireland, however The Sex Discrimination Gender Reassignment Regulations (Northern Ireland) 1999 does.
The Act was repealed in full by the Equality Act 2010.
A person discriminates against a women if on the ground of he treats her less favourably than he treats or would treat a man( Sex Discrimination Act 1975, s.1(1)(a)). A claim regarding direct discrimination involve a ‘ comparator’. the case of Shamoon -v- Chief Constable of the Royal Ulster Constabulary the House of Lords explained the significance of identifying an appropriate r comparator in direct discrimination cases.
The need for a comparator has been one of the most problematic and limiting aspects of direct discrimination(Sandra fredman, p 96) as states in statutes about discrimination regarding grounds of sex and race.The requirement is less harsh than in the legislation about equal pay, as the provisions about discrimination on grounds of sex and race permit a “hypothetical” comparison, based – in a sex case, Nevertheless the choice ofcomparator requires that a judgment must be made as to which of the differences between any two individuals are relevant and which are irrelevant. The choice of characteristics may itself be determinative of the outcome (Advocate General v MacDonald 2001 SC 1 and Pearce v Governing Body of Mayfield School  EWCA Civ 1347;  ICR 198.) This suggests that care must be taken not to approach this issue in a way that will defeat the purpose of the legislation, which is to eliminate discrimination against women on the ground of their sex in all the areas with which it deals.( http://www.publications.parliament.uk/pa/ld200203/ldjudgmt/jd030227/sham-2.htm)
Regarding Equal pay, when comparing to other types of discrimination law, the claimant have to show an actual comparator, they cannot merely show hypothetical one. In Walton Centre for Neurology v Bewley (2008 IRLR 588 EAT). The EAT held, that it was not possible to use a successor as a comparator in a claim for equal pay. According to Hayward v Cammel Laird Shipbuilders Ltd (1988 ICR 464 HL) The equal pay legislation allows a comparison to be made between each term in the employment contract. Further difficulty in this area is that the claimant and the comparator must work for the same employer. This will put people working in places like NHS at a difficult situation, in discovering who the employer is, as there have been, many amendments in organisational structure recently. In Leverton v Clwyd County Council  ICR 33 HL, as both persons had been arranged by the same collective agreement it was accepted that they had common terms. However, claimants are able to select a comparator that works for a third party employer who is not connected with the claimants employer, yet in order for that to be possible their employment terms must be of a common source( Article 141 of the EU Treaty) In the case of Lawrence & others v Regent Office Care Ltd & others. Although the comparisons allowed under Article 141 are not restricted to the situation where the Applicant and her comparator work for the same employer, it is necessary to identify a single source that is responsible for the difference in pay, ie, the inequality, which could restore equal treatment.( www.equalityni.org/archive/word/Aug04Casestudiesequalpay.doc)
In some situations there are no appropirte compactor especially in discrimination reagarding preganancy. Indeed , this difficulty has been sufficiently acute to prompt a reformulation of the equality principle liberating it from the need for a comparator and in the early pregnancy cases it was hekd that since there was no appropriate male comparator to a pregnant woman, pregnancy was simply excluded from the protection of the sex discrimination legislation.( fredman p 99). The UK courts focused on the ‘relevant circumstances of teh appropriate comparator under ss. 5(3) of the SDA, and defined those circumstances so as to defeat direct discrimination claims based on pregnancy.( p 53, aileen. In the case of Grant v South West Trains C-249/96 ECR I-3739
In relation to the area of disability claims, the need for a comparator is much easier when comparing with Equal pay Yet it is also kind of difficult because the Disability Discrimination Act is created in a different way from other legislations. In Clark v TGD Ltd Novocold (1999 IRLR 318) the Court of Appeal considered a cruel approach,: The comparator was a non-disabled person. Clark was discriminated as the court held a non-disabled employee wouldn’t be absent and would work and therefore would not have been dismissed, however along came London Borough of Lewisham v Malcolm  UKHL 43 where it was held that the comparator should be in the similar factual state as the claimant. They said that that the comparator will still be a non-disabled person however who had been absent from work for a same length of time and if that person is dismissed, then there’s no discrimination.