Tinglan Hong granted anti-harassment order by the high court after being besieged by photographers 

Hugh Grant had been forced to employ round-the-clock security guards to protect Tinglan Hong, his lawyer said. Photograph: Dan Kitwood/Getty Images

 Tinglan Hong, the mother of Hugh Grant's daughter, has been forced to seek an anti-harassment order against paparazzi who she says have been harassing her since the birth of her baby.

An order granted on Friday by Mr Justice Tugendhat at the high court of justice in London means that anyone harassing Hong or her baby daughter – or encouraging or helping others to do so – risks being imprisoned, fined or having their assets seized.

Mark Thomson, the solicitor acting for Hong, said: "The means that some of these photographers have used to get pictures for the tabloids are utterly appalling.

"Today's injunction stops paparazzi pursing her, doorstepping her, harassing her, following her or putting her under surveillance."

It is understood that the detailed, five-page injunction also forbids photographers approaching within 100 metres of Hong's home or taking pictures of her when she is with family and friends, in any building not open to the public, or while she is being followed or pursued by other photographers.

Thomson said the severity of the order was an indication of the level of harassment Hong has been suffering. "It appears that Tinglan has been under media surveillance since [her relationship with Grant was revealed in] January," added Thomson. "Tinglan has been literally under siege since the newspapers announced the birth [in November]."

Because of the harassment Grant has been forced to employ security guards to protect Hong at her home round the clock. When that failed to defuse the attention, he engaged his own lawyer, Thomson, to argue for the injunction.

"Hugh Grant is genuinely worried. He wants his child to be protected," said Thomson. "It's outrageous behaviour [on the part of the press]."

The need to seek an injunction to protect his daughter and former partner will strengthen Grant's determination to force a change in the attitude towards privacy intrusion of some members of the media.

Grant became the public face of the Hacked Off campaign against phone hacking this summer. He said he was convinced his phone was routinely hacked by journalists and is leading the fight to end what he calls a "culture of privacy intrusion" by some members of the press.

The actor is one of 46 alleged victims of media intrusion – along with Harry Potter author, JK Rowling, actor Sienna Miller, Formula One boss Max Mosley and the parents of Madeleine McCann and Milly Dowler – who will give evidence at the Leveson inquiry into alleged media intrusion into their private lives.

He has yet to seek civil damages from any media organisations because, he said, he would be able to speak "with a cleaner voice" if he had not made any financial benefit from the scandal.

Grant met the prime minister in October to press his case for tighter regulation of Britain's news industry after joining forces with Hacked Off to call for an end to the excesses of the tabloid press.

He was invited to meet David Cameron after taking his film-star glamour to all three main party conferences. At conventions in Liverpool, Manchester and Birmingham, Grant accused tabloid newspapers of having a business model of "privacy theft for profit".

To packed meeting halls, he attacked politicians for their "craven" approach to Murdoch, whose support, he said, could help to swing elections. "Five successive governments licked the boots of one particular media owner," he said.

Sitting on panels alongside campaigners from English PEN and Index on Censorship, Grant insisted he was prepared to fight a "time-consuming, long-grass operation" to show how widespread the problem of press intrusion is.