There were 170 complaints about the promotion which promised people a £500 mystery prize, according to the industry regulator.

It is completely unnecessary to hassle people this way

Mobile phone user Simon Cullen

People were told they would win the prize if they dialled a premium rate number and answered a question correctly.

But those who called, were told they had actually won discount holiday vouchers worth up to £500, according to the industry regulator.

An investigation has been launched by the Independent Committee for the Supervision of Standards of Telephone Information Services (Icstis).

Holiday vouchers

Spokesman Rob Dwight told BBC Radio Five Live's Breakfast that it had been inundated with complaints about the promotion by the Leeds-based company Moby Monkey.

"One hundred and seventy odd complaints about one premium rate service is huge.

"The range of complaints varies from people who just aren't happy with their mobile numbers being used in this way right through to people who are very angry at the seemingly misleading nature of the text message promotion," he said.

Those dialling the premium rate number, which is charged at £1.50 a minute and lasts three or four minutes, are then told what they have won is not cash but holiday vouchers for sometimes as little as £125.

Icstis says many more people will have deleted the message or not know how to contact them.

Parents whose children - in one case as young as 11 - have received message are among those who have complained.

Other people say they get the message over and again - in one instance up to 40 times in a day.

Night-time calls

Calls were also made in the middle of the night.

And one company said 25 of their corporate phones with sequential telephone numbers had received the message at the same time.

Five Live's Philippa Busby said that this raised the question whether or not the company had followed the code of practice which says unsolicited text messages must be dialled manually rather than by using a computer.

Simon Cullen, who was one of those who received the messages, told the programme: "It is completely unnecessary to hassle people this way. My phone is private."

The Moby Monkey website is currently unavailable with a message saying it has been suspended.

The company itself was uncontactable.

Five Live contacted some of the holiday companies mentioned with regards the holiday vouchers.

All of them said the promotion was nothing to do with them.