A government agency has apologised to the victims of a violent stalker after border staff let him into the country.

The UK Border Agency has written to the family of Dr Alison Hewitt, who was subjected to a four-month stalking campaign by her jilted lover, Al Amin Dhalla.

Dr Hewitt’s mother, Pamela Hewitt, had written to the agency in November 2010 warning them about Dhalla.

The letter warned the agency that he had an extensive criminal record for violence, was banned from the US, used three aliases and had previously entered the UK illegally.

Despite giving the agency his passport number and flight details of when and where he would return to Britain, Dhalla was able to walk through immigration unhindered and begin a terror campaign against the family.

However, the agency defended its failure to prevent him re-entering the country by saying the Canadian national had failed to declare his previous convictions when applying for a visa.

The agency also said that they would seek to deport Dhalla, nicknamed the crossbow stalker, at “the earliest opportunity”.

Dhalla and Dr Hewitt first met through an exclusive dating agency in 2009 but the family became suspicious over lies Dhalla told about his background, including not disclosing a conviction in Canada for assaulting his uncle with a weapon.

Around the same time that Mrs Hewitt wrote to the Border Agency, her daughter ended the relationship.

Dhalla at first refused to move out of her home, forcing Dr Hewitt’s relatives to evict him and days later poison pen letters were sent to Dr Hewitt’s NHS employer. In a four-month terror campaign, he tried to burn down the home of Dr Hewitt’s mother and stepfather and hired a private investigator to snoop on her.

He was arrested at Princess Royal Hospital in Haywards Heath, where Dr Hewitt worked. Police found a loaded crossbow, a large knife and a fuel-soaked envelope addressed to Mrs Hewitt in his car. He was given an indeterminate sentence in June and will serve at least six years in jail before he is even considered for release.

A UK Border Agency spokeswoman said: “We believe all foreign criminals should be removed from the UK and we will seek to deport Mr Dhalla at the earliest opportunity.

“All passengers entering the UK are checked against a watchlist. Where a previous criminal conviction is identified, or we are made aware by foreign law enforcement agencies that an individual may pose a risk, this may be grounds to refuse entry.”