Gavin Williamson told to ‘focus on his job’ and accused of giving credence to ‘false and ridiculous smears’ in Sun story

Labour has criticised the defence secretary, Gavin Williamson, for seizing on controversial claims that Jeremy Corbyn had unwittingly met a Czech spy posing as a diplomat in the 1980s.

After the Sun’s front-page report on Thursday, Williamson, who was attending a Nato meeting in Brussels to discuss international cyber security, said it showed Corbyn “cannot be trusted”.

In response, Labour told the minister to “focus on his job” and accused him of giving credence to “false and ridiculous smears”.

The Sun had reported that Czech intelligence files from the cold war showed that Corbyn met an agent posing as a diplomat called Lt Jan Dymič on three occasions in 1986 and 1987, on two of which other people were in attendance.

A spokesman for Corbyn told the newspaper that the then backbench MP had met a Czech diplomat – who did not use the name Dymič – for a cup of tea in the Commons in the 1980s. They added that Corbyn had never knowingly talked to a spy, and said that that any claim he was “an agent, asset or informer” was “a ridiculous smear”.

Corbyn has faced a string of personalised attacks which start in the rightwing media, typically focused on his time as a leftwing backbench MP in the 1980s and 1990s, and are followed up by Tory politicians.

The Sun said Czech intelligence gave Corbyn the code name COB. In 1986, the Czech files noted the Labour MP was “negative towards USA, as well as the current politics of the Conservative government”.

A note of a meeting in October 1987, lasting from 4pm to 5.30pm, said “the topic of discussion” was the “national liberation movement, the position of Britain and USA concerning the situation in BSV or Persian Gulf. Knowledge could not be utilised for the purpose of information as they were limited to general nature”.

Williamson said: “Time and time again he has sided with those who want to destroy everything that is great about this country, whether it is sympathising with terrorists, backing rogue regimes, or cosying up to those who want to inflict pain and misery on the British people.”

Williamson is under scrutiny for refusing to answer questions from the Guardian about his brief relationship with a female office colleague in 2004, when he was married. The would-be politician left fireplace firm Elgin & Hall shortly afterwards, but has refused to give details of the terms on which he departed or whether he received a pay-off.