In July 2010, still flushed with general election victory, David Cameron headed to India on his first big trade mission.

It was, we were told, the largest business delegation a British prime minister had ever taken abroad.

He promised to double trade with India by 2015.

More than two-and-a-half years on, Mr Cameron is back in Mumbai and, while the delegation of chief executives and vice chancellors is even bigger, the promises are the same.

Britain is, he says, on track to meet its target of doubling trade with India by 2015.

'Low base'

But as several businessmen on the plane told me, it was starting from a pretty low base. Belgium trades more with India than we do.

We trade more with North Rhine Westphalia than with India.

So when Mr Cameron talks of "untapped potential" and there being "much more to do", he is speaking with some degree of understatement.

Since 2010, firms like BP and Diageo have made some big investments. But that first prime ministerial trip failed to generate as many deals as had been expected.

Famously Delhi chose to buy more than a hundred French Rafale fighter jets - as seen in Mali in recent weeks - instead of the part-UK produced Eurofighter Typhoon.

For the economy to recover, for some growth to re-emerge, he needs trade missions like this to succeed

And for several big firms, trade with India has been marred by billion-pound tax rows and unpaid fees.

In recent weeks, it also emerged that a multi-million pound deal to provide India with 12 AgustaWestland helicopters had been put on hold amid bribery allegations - claims the firm denies - putting jobs at risk in Yeovil.

So when David Cameron says he wants Britain and India to forge one of the great partnerships of the 21st Century, he knows he has some work to do.

This may be the largest prime ministerial delegation ever, but it arrives in Mumbai on bended knee.

Yes, the UK clearly has much to offer that India needs, in terms of expertise in infrastructure, engineering and universities.

And yes, at Unilever's Mumbai headquarters on Monday morning, Mr Cameron urged Delhi to open its markets up to greater foreign trade, particularly in financial services like banking and insurance.

But it is noticeable that his first substantive announcement is one designed to reassure - a promise that Indian businessmen will get a new, fast-track visa service so they can get on a plane fast to the UK.

Mr Cameron also clarified the mixed messages over immigration by telling Unilever workers there would be no limit to the number of Indian students who could come to the UK.

He also promised up to £1m to help fund a feasibility study into using British expertise to develop a so-called "business corridor" between Mumbai and Bangalore.

Strategy change

On the Eurofighter deal, despite the somewhat optimistic briefing, the prime minister will simply remind his Indian counterpart that the European offer stands if the French bid were to fall through.

But he will not push for fear of insulting his hosts.

What is different is the change in strategy.

Instead of just focusing on big name British companies to sign big ticket deals, Mr Cameron has brought with him 30-odd small- and medium-sized firms in the hope that they can inculcate a new generation of trade and entrepreneurial links with India.

And let us not forget how important this all is for Mr Cameron.

For the economy to recover, for some growth to re-emerge, he needs trade missions like this to succeed.

So this probably won't be his last trip to India.