Louise Haigh has resigned as transport secretary after it emerged she has a fraud conviction for wrongly reporting her work mobile phone stolen in 2013.

She said in a letter to the prime minister published on Friday that she is “totally committed to our political project” but believes “it will be best served by my supporting you from outside government”.

“I am sorry to leave under these circumstances, but I take pride in what we have done. I will continue to fight every day for the people of Sheffield Heeley who I was first and foremost elected to represent and to ensure that the rest of our programme is delivered in full,” she wrote.

Earlier, it emerged she had been convicted by Camberwell Green magistrates and given a conditional discharge after pleading guilty to an offence in connection with misleading the police.

The incident happened when Haigh was in her 20s and was mugged on a night out while working for the insurer Aviva. She gave police a list of items she thought were missing from her handbag, but wrongly included her work phone which at the time she thought had been stolen.

Haigh was issued with a new phone but when she subsequently found her old work phone and turned it on, the police called her in for questioning.

In response to her resignation letter, the prime minister, Keir Starmer, wrote: “Thank you for all you have done to deliver this government’s ambitious transport agenda.

“You have made huge strides to take our rail system back into public ownership through the creation of Great British Railways, investing £1bn in our vital bus services and lowering cost for motorists.

“I know you still have a huge contribution to make in the future.”

Haigh disclosed the conviction to Starmer when she was first appointed to his shadow cabinet and sources said he was supportive of her. As the conviction has now been spent it is no longer on her record.

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