LONDON (AFP) - Britain could shortly place France on a travel "red list" and tighten Channel border controls due to the risk of new coronavirus variants, Prime Minister Boris Johnson said Wednesday (March 24).

France is struggling with a third wave of cases and on Wednesday expanded virus lockdowns to three more areas including the city of Lyon.

The prevalence in France of cases of South African and Brazilian variants, which are potentially more transmissible, has caused particular concern.

Asked by senior MPs why France was not on Britain's travel "red list", Johnson said that this was "something we will have to look at" while warning it would cause disruption, particularly to cross-Channel trade.

Travellers from red list countries cannot enter the UK unless they are British or Irish nationals or have residence rights, in which case they have to pay to quarantine in hotels.

Johnson acknowledged that "we have to look at the situation at the Channel".

"We can't rule out tougher measures and we will put them in if necessary," he said.

Questioned on the need for tighter controls such as testing of lorry drivers arriving at Channel ports, Johnson told senior MPs that there was a need to balance the risks of "very serious disruption" to the flow of goods such as food and medicine.

Hauliers are currently exempt from quarantining and testing measures, Johnson said, warning of delayed supplies if this changed.

When France introduced compulsory testing of lorry drivers arriving from the UK in December, it caused huge queues of lorries in southern England.

"We will take a decision, no matter how tough, to interrupt that trade, to interrupt those flows, if we think that it is necessary to protect public health and to stop new variants coming in," Johnson said, however.

"It may be that we have to do that very soon." England's chief medical officer Chris Whitty and his deputy Jonathan Van-Tam have reportedly put pressure on Johnson to bring in stricter border controls.