To the untrained eye, these cards look authentic – European driving permits, students' union cards and national identity documents.

However, they are all fakes, bought online for a few pounds by children who use them to try to trick their way into a pub, or con their local shopkeeper.

Police showed the Leicester Mercury just a small sample of the fake "proof of age" cards handed to them by security staff at city nightclubs.

The most common are driving permits or national or European identity cards. Some teenagers had tried to use students' union cards for universities which do not exist.

Pc Sean McOwen, of city centre police, said: "The fortunate thing is that door staff are seizing these cards to prevent the young people going anywhere else with them. They are handing the cards to us and we're getting a steady flow of them now, probably 10 a month."

The plastic cards, some of which have been given sophisticated touches such as holograms, are made to order over the internet.

Children only have to submit passport-style photographs of themselves and choose a date of birth which makes them appear to be over 18. The cards, which cost between £10 and £15, are then mailed to them in plain brown envelopes.

Firms selling the cards are able to protect themselves by including warnings on their websites that the documents are "novelty items''.

Since they are not providing counterfeits of real forms of identification, they are not breaking any laws.

Police have highlighted the problem to warn parents that their children may be tempted to buy fakes online – and that using fake IDs to buy alcohol or cigarettes is a criminal offence.

Where cards carry real addresses, officers can contact the child's parents. Pc McOwen said the cards were regularly destroyed.

Neil Jennings, regional manager for Nexum Leisure, owners of Zanzibar nightclub in Gravel Street, Leicester, said: "There are all sorts of shenanigans going on with fake ID. We see the European driving permit quite a bit."

However, the dozen companies whose sites the Leicester Mercury looked at stressed their use by under-18s to get into pubs or nightclubs was illegal.

A spokesman for one of the firms said his website made it clear that the cards were for novelty purposes.

He said: "We're within the law because we state quite clearly on the site that they are not to be used to buy age-specific products like alcohol or tobacco.

"Some kids will try it, though, I'm sure. All of the companies which offer this service make sure that something like 'this is a novelty item' is printed on the back."