To be successful in a claim for direct discrimination, you must be able to show that:
There was less favourable treatment on the grounds of gender, being married or having a civil partner, race, religion or belief, sexual orientation, age, disability, gender reassignment, pregnancy or maternity.
The treatment you received was different to the treatment of others. It is not enough to be simply unfairly treated - you have to show that the treatment was a direct result of protected characteristics noted above.
It is also useful (though not essential) to have a real-life comparator.