The watchdog says its research could suggest discrimination by the dating app and a breach of UK law.

Which? asked almost 200 mystery shoppers to create real profiles and make a note of prices quoted for Tinder Plus - a premium package with perks such as unlimited "Likes" and "Rewinds" and the ability to undo accidental selections.

It showed some gay and lesbian users were paying more, with an average premium of more than 10% (£6.74) compared to bisexual users, and more than 8% (£5.28) compared to heterosexual users.

This trend was driven by the youngest age group, with Which? finding that gay and lesbian people aged 18 to 29 paid £60.15 on average - 37% more than heterosexual users aged under 30 (who paid £44.06 on average) and 30% more than bisexual users under 30 (£46.09).

When it came to age, those in the 30 to 49-year-old age bracket paid 48% more - a £24 difference - and the over-50s paid 46% more - a £23.19 difference - on average for a 12-month Tinder Plus subscription.

Which? said it had reported its findings to the Equality and Human Rights Commission (EHRC) and the Information Commissioner's Office.

The group's director of policy and advocacy, Rocio Concha, said the research suggested "unlawful price discrimination", whether or not it is intentional on Tinder's part, and potentially unlawful processing of personal data.

"If regulators decide that Tinder's personalised pricing is breaking the law, then the dating app giant must face strong action."

Tinder said it was "categorically untrue that our pricing structure discriminates in any way by sexual preference".

It told Which? that older people did have to pay more in some countries, but said the price difference was "a discount for younger users".

The Equality Act 2010 makes it unlawful to charge people of one sexual orientation more than others unless there is a clear justification for this.

The consumer group noted that it was occasionally justifiable under UK law to offer age-based price variations for the same product or service, such as discounts to over-65s or students, where it can be shown there is a legitimate basis for this.

However, it said that in the case of Tinder it was unclear as to why over-30s were paying more.

What has Tinder said about the claims?

A Tinder spokeswoman told Which?: "Tinder is free to use and the vast majority of our members enjoy our app without upgrading to the paid experience.

"However, we do offer a variety of subscription options to help our members stand out and match with new people more efficiently.

"Tinder operates a global business and, in some geographies, we offer discounted subscriptions to younger members.

"In addition, we frequently offer promotional rates which can vary based on factors like location or length of subscription. No other demographic information is considered in our pricing structure."

An EHRC spokeswoman said: "As Britain's equality regulator it is our job to protect, uphold and enforce equality laws. We take reports of discrimination very seriously.

"This report of potential discrimination by Tinder is concerning. We will consider these findings by Which? and respond in due course."