Question to the Home Office:

To ask the Secretary of State for the Home Department, whether it is necessary for applicants for a visa to visit the UK to show that they have booked a return air ticket when they apply for the visa.

Applicants must satisfy the Entry Clearance Officer that they are genuinely visiting the UK for a period of less than six months, and intend to leave the UK at the end of their proposed visit. To support their visa application, applicants may wish to submit documents setting out accommodation and return travel bookings. However, applicants are advised not to make any payments for accommodation or travel until they have received a visa.

Guidance on the types of supporting documents that applicants can provide as part of their visa application is available on the UK Visas and Immigration page of gov.uk:
https://www.gov.uk/government/publications/visitor-visa-guide-to-supporting-documents.