BRITAIN (REUTERS) - British Foreign Secretary Boris Johnson on Wednesday (Jan 12) compared any attempt to punish Britain for leaving the European Union to a World War Two escape movie, saying both sides would do better to strike a mutually beneficial trade deal.

Speaking in New Delhi a day after Prime Minister Theresa May laid out the case for a "hard Brexit", in which Britain leaves the European single market, Johnson said attempts to curb free trade cut both ways.

He was answering a question on comments made earlier by an aide to French President Francois Hollande who said Britain should not expect a better trading relationship with Europe once it was outside the common market of 500 million people.

Johnson's comments to the Raisina Dialogue, a geopolitical conference hosted by the Indian foreign ministry and the Observer Research Foundation, will be scrutinised back home to see whether he is straying from May's message, delivered in a landmark speech in London on Tuesday (Jan 17).

In his prepared remarks, Johnson - a leading face of the successful campaign to vote "leave" in a referendum last June - said Britain should embrace free trade not only with Europe but with the wider world.

Turning to India, Johnson endorsed Prime Minister Narendra Modi's call for tension in the South China Sea to be addressed under a rules-based order and said Britain stood with India in its fight against terrorism.

But, complaining of the 150 per cent import tariff India charges on Scotch whisky, he said it was time for Britain and Asia's third-largest economy to strike a free trade deal.

That won't be possible until after Britain leaves the EU, which must happen within two years of launching formal exit talks. But it would at least be possible to make a start.