Claimants in employment tribunal cases can sometimes receive legal representation from their trade union.
You may also find that some solicitors offer Damages Based Agreements or Conditional Fee Agreements in relation to employment matters.
It is also possible to obtain legal assistance via Civil Legal Advice who provide government funded assistance (‘legal aid’). This is in relation to discrimination matters only: https://www.gov.uk/civil-legal-advice
You could also engage a solicitor and pay privately for this. At Minster Law, we can offer to act for clients on a private basis in some cases. Other solicitors can be found via the law society website.