It is an increasingly common message from websites: browse for free - if you allow us to track your data and target you with personalised ads - if you don’t, hand over some cash.

The model is known as “consent or pay” and, while it may be becoming increasingly common, questions remain over whether it is ethical or even legal.

The UK data regulator, the Information Commissioner’s Office (ICO) has launched a consultation on the practice - it will report its findings later this year.

“In principle, data protection law does not prohibit business models that involve ‘consent or pay,’” the ICO says on its website.