STICKERS that act as credit cards for small transactions will be launched today by Barclaycard.

Its new “Paytag” is one third of the size of a normal bank card, and the company hopes users will stick it to the back of their mobile phones.

It is the latest in a number of attempts by companies including Orange, O2 and Google to encourage people to pay with “contactless” technology that does not always require a PIN code.

Barclaycard says that 150,000 contactless payment terminals will be in shops including Waitrose, Tesco, Mcdonald’s and Eat by the end of the year, but it has not released figures on how many people are using them.

An existing £15 limit for contactless payments will rise to £20 in June. London buses will use the technology by the end of the year, with the rest of the capital’s transport network following in 2013.

Questions have been raised about the security of the system, but an investigation by Viaforensics, a mobile phone security firm, found that only a small number of the 15million contactless cards in circulation could easily be accessed by fraudsters. All fraud is covered by the card companies’ standard policies.

Many customers do not know that their cards already have the technology.

David Chan, head of Barclaycard Consumer Europe, said that Paytag would complement traditional credit cards, and was just as secure. He said the company had done “huge amounts” of research to prevent the devices falling off, and to make sure they did not leave sticky marks on users’ phones.

Mr Chan conceded that Paytag was a halfway house until payment technology was built in to phones.

A study carried out for Barclaycard predicts that £3billion worth of purchases will be made with mobile phones in Britain in 2016.

The Paytag will be offered free to all existing Barclays customers, beginning today with a first, smaller group of customers.