An appeal has been launched after a passenger witnessed a teenager performing a "sex act" after getting on the train at Newcastle.

Police are searching for the teen, 17, after he carried out a sex act opposite a woman on a 2:28pm service from London King's Cross to Ediburgh Waverley this month (March 10).

British Transport Police (BTP) have urged anyone who witnessed the incident to contact them.

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Police have said the woman witnessed the boy carrying out the act between 5:50pm and 7:30pm, before leaving the service at Edinburgh.

He is described as being aged 17 to 18, white, 6ft, of proportionate build, with sandy hair shaved at the side and longer on the top.

In a statement, a BTP spokesperson said: "British Transport Police have urged anyone who witnessed the incident, which occurred on March 10 on the 2.28pm service from London King’s Cross to Edinburgh Waverley, to contact them.

"Police said the teenager sat opposite the woman after the train stopped at Newcastle, and between 5.50pm and 7.30pm she saw him carrying out the sex act.

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"He left the train at Edinburgh."

He was also wearing a 1990s-style multicoloured, patterned bomber jacket with black across the shoulders, a bright purple T-shirt and loose-fitting blue jeans.

Anyone who witnessed what happened or has any information about it is being asked to contact British Transport Police by calling 0800 40 50 40 or texting 61016, with reference 2300028810.