Myleene Klass was said to be "aghast" and "bemused" today after being warned by police for waving a knife at youths who entered her garden.
The TV star and Marks & Spencer model was in the kitchen with her daughter upstairs when she spotted the teenagers peering into her window just after midnight on Friday. She grabbed a knife and banged the windows before they ran away.
Hertfordshire Police officers warned Miss Klass she should not have used a knife to scare off the youths because carrying an "offensive weapon" - even in her own home - was illegal.
Her spokesman Jonathan Shalit said the former Hearsay singer was "utterly terrified" and was stepping up security at the property near Potters Bar.
He told the Sunday Telegraph: "Myleene was aghast when she was told that the law did not allow her to defend herself at home.
"All she did was scream loudly and wave the knife to try and frighten them off.
"She is not looking to be a vigilante, and has the utmost respect for the law, but when the police explained to her that even if you're at home alone and you have an intruder, you are not allowed to protect yourself, she was bemused."
Miss Klass' fiance Graham Quinn was away on business at the time of the scare.
It came amid calls for greater rights for people to defend themselves against intruders on their property.
Last month when Munir Hussain was jailed for beating a man who tied up his family in their home. He and his brother used a cricket bat to beat one of the intruders.
The case prompted the Conservatives to pledge they would make it harder for people who tackle burglars to be prosecuted.
A spokeswoman for Herts Police said no reference was made on the Klass incident report about a weapon.
She said: "We got a call at 12.45am (on Friday) to reports of the owner of the property hearing noises outside their address.
"They had been there for 45 minutes.
"Officers were in attendance and checked the property.
"There was no one around although they could see footprints in the snow.
"No property had been taken and there were no intruders.
"It was treated as a trespass incident.
"Words of advice were given in relation to ensuring suspicious behaviour is reported immediately."
A Ministry of Justice spokesman said: "The Government strongly supports the right of law abiding people to defend themselves, their families and their property with reasonable force.
"That is why we introduced the self defence provisions of the Criminal Justice and Immigration Act 2008.
"These made it clear that as long as they use reasonable force to protect themselves or others, people should have confidence that the law will support them. The level of force used should not be excessive or disproportionate in the circumstances as they viewed them.
"What the law does not permit, however, is an act of revenge.
"Punishment of criminals is rightly a matter for the courts: it is not for victims, vigilantes or anyone else to take the law into their own hands by seeking to punish an offender for a crime committed against them, their friends or family."