Police have warned they will come down hard on anyone inventing fictitious robberies after a rise in the number of claims.

They issued the warning after giving a woman an on-the-spot fine over one bogus claim. They are currently investigating two other potentially fictitious muggings. The woman said she had been robbed of £500-worth of jewellery, in November in Cowley, Oxford.

But it turned out she had in fact lost the valuables and decided to tell police she was mugged so that she could claim money on her insurance. She was given an £80 fine by officers.

A 14-year-old boy is at the centre of another police investigation after alleging he was robbed in Turl Street, Oxford, while another schoolboy is to be questioned by officers over a claim he was threatened and robbed in Barns Road, Cowley.

It is suspected the first boy had stolen the money from his family and said he was robbed after the theft was discovered, police spokesman Toby Shergold said.

He was speaking after Victoria East, 23, of Trevor Place, Oxford, was convicted at Oxford Crown Court for perverting the course of justice after making a false robbery allegation.

East said she was threatened with violence and had items stolen, including a medical prescription.

Police made two arrests before discovering she had made up the story in an attempt to get another prescription. She was sentenced to 100 hours' community service and given an 18-month supervision order.

Anyone found guilty of making a false claim and wasting police time faces an £80 on-the-spot fine or even jail.

Dick Evans, a case investigator with the Oxford police robbery team, said: "The number of false robbery allegations is very concerning and appear to be on the increase, especially around the festive period when money can be short.

"Robbery is a serious offence and one that police spend a great deal of time investigating. We will deal robustly with those who make false allegations."

Mr Evans added: "The last thing we want to do is discourage genuine victims of crime contacting the police.

"But we want to warn those people who might consider making a false crime report that all such incidents are thoroughly investigated and anyone discovered to be attempting to mislead the police will face a fine, a criminal conviction or even imprisonment."

Anyone with information that could assist the police can call Mr Evans at Oxford police station on 08458 505505 or anonymously to Crimestoppers on 0800 555111.