The Mayor has been called on to provide greater clarity around the junk food advert ban on Transport for London (TfL) networks.

The ban began today after originally being proposed by Mayor of London Sadiq Khan last year.

This means adverts for foods that are high in salt, sugar and fat will not be allowed on the London Underground, Overground, buses, TfL Rail, trams and rivers services.

During a London Assembly Meeting earlier today on Mr Khan’s budget, Conservative London Assembly Member Andrew Boff asked Mr Khan exactly which companies he wanted to see stop advertising junk food.

Mr Boff said: “Last year you said junk food companies make millions of pounds advertising to children, which companies are these?”

Mr Khan said he would send Mr Boff a list but refused to name any companies during the meeting, telling the Tory politician it was “not hard to work out”.

He added: “You just have to see what companies sell junk food and advertise with us, then you can work backwards.

“This move is as much about banning the advertising of a produce high in salt and sugar rather than banning a whole brand from advertising.

“I will not apologise for banning foods high in salt, sugar or fat.”

But Mr Boff accused Mr Khan of “refusing” to respond to the questions.

He replied: “While everyone agrees that we need to help kids to live healthier lives, there is no evidence to suggest that this ban will have any impact on the scourge of childhood obesity.”

Mr Boff also wanted to know why Mr Khan was banning junk food adverts but had allowed a doughnut cart to be installed at Oxford Circus Tube station today – something which was revealed in a Tweet by a Conservative councillor in Westminster.

He added said: “You allowed the installation of a doughnut stall at Oxford Circus Tube station, you are taking rent from this stand and yet you are not going to ban it.”

The ban also came under fire from advertising agency Outsmart who said the ban was rooted in “political gain” not fact.