Daren Timson-Hunt pleaded guilty last week to “operating equipment” beneath another person’s clothing while at Embankment underground station on 1 July.
The 54-year-old followed a woman who left a Northern Line train at the station, Westminster Magistrates Court heard.
He then waited at the bottom of a flight of stairs and waited until the woman climbed to the top of the steps before pulling his phone out.
Another passenger saw Timson-Hunt hiding his phone under his leg to take a photo of the woman.
Upskirting refers to surreptitious filming or taking photographs under an individual’s clothing without consent.
The practice became a crime in April, under the Voyeurism [Offences] Act 2019.
People found guilty of the crime can receive a sentence of up to two years in prison and in the most serious cases they could be placed on the sex offenders register.
The British Transport Police said the conviction was the first to be obtained under the new law in England and Wales.
Timson-Hunt was banned, pending sentencing on Thursday, from travelling on the underground except for a medical or solicitor’s appointment, court hearing or job interview.
He was also barred from carrying a device capable of recording an image in a public place.
A spokesperson for the Department for International Trade confirmed on Monday that the 54-year-old had worked as a government lawyer until he resigned in August.
The New Statesman reported that the lawyer was involved in Brexit negotiations as head of the EU Exit and Goods Legal team.
Timson-Hunt also served as a governor at a primary school in Essex but resigned from his post in June.
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Additional reporting by agencies