If you lose the case, you can request the tribunal to review its own decision. You must do this at the hearing or within 14 days of the decision being recorded. The grounds for doing this are limited though. You may have a good chance of success if, for example, one of the parties was absent for part or all of the hearing, or if new evidence becomes available (but not simply because you thought the decision was wrong). Your employer can also appeal.
Appeal is also possible to the Employment Appeal Tribunal (EAT) which sits in London for England, Cardiff for Wales and Edinburgh for Scotland. The EAT is a special appeal tribunal which only deals with employment related issues, nearly all on appeal from the Employment Tribunals. The appeal has to be lodged within 42 days of the tribunal decision. A special form is required, which can be obtained from the Employment Tribunal office or directly from the EAT.
Appeals are only allowed on a point of law but this can include a 'perverse' decision by the tribunal where, for example, the members did not understand the facts.
You will need a copy of the full written reasons for the tribunal's decision, which they will send you automatically and a copy of the employment judge's notes, which you will have to request from the tribunal.
It is possible to get legal aid for representation at the EAT and, as it will essentially be dealing with points of law, it is important to be properly represented by your union or by a solicitor. Unions may have in-house solicitors who will represent you, or may engage a solicitor for you and pay the costs.
Appeal from the EAT is to the Court of Appeal, but you need leave from the EAT to do this. Appeal from the Court of Appeal is to the Supreme Court. You will certainly need legal representation at these stages.
It is also possible for a tribunal (or any of the courts involved) to refer a case to the Court of Justice of the European Union (CJEU). Only cases involving a principle of European law, that has not already been established, will be referred to the CJEU. It is likely to be a slow and expensive process, in which you will need the support of your union, or an organisation such as the Equality and Human Rights Commission.
