Last Night's TV - Theo's Adventure Capitalists, BBC2; The Boats That Built Britain, BBC4; The Story of Science – Power, Proof and Passion, BBC2

Risky business as yeast meets West

I think a lesser woman would have wilted when the scabby dog said no. Cheryl Calverley, marketing manager for Marmite, was in Mumbai on a mission – nothing less than opening up the sub-continent for Britain's best-loved savoury treacle. Local knowledge, in the shape of Unilever's Indian executives, had said it couldn't be done. But Cheryl and her boss, Matt, Marmite's managing director, were convinced, like other merchant venturers before them, that great riches lay to the East, and Theo's Adventure Capitalists was following their progress. First task – hit the streets with a tray of Marmite sandwiches and see what the locals make of it. They made faces mostly, and not blissful "where can I buy this stuff?" faces either, but the kind of alarmed rictus that you display when you've bitten into a bad oyster. Theo Paphitis – on hand to mentor three groups of of what he calls "ontroppenurrs" – held out a sarnie to a passing pi-dog. It sniffed, backed away, and cocked a leg on a nearby car. Cheryl, to her credit, roared with laughter.

Cheryl seems to think of herself as a kind of Lawrence of Arabia of grocery retail, talking about the challenge of conquering this virgin territory with a passionate intensity that must surely tip the odds in her favour. "My God, that would be an incredible legacy," she said dreamily, contemplating a future world in which Marmite would be indispensable from Kashmir to Kerala. And Cheryl's adaptability – when it became clear that you couldn't even give the product away to the dogs in the street – was impressive. If she couldn't persuade people to put it on their toast (is it a big toast nation, India?) then perhaps, she thought, they could be convinced that it is a cooking ingredient. One tasting session later ("the biryani was absolutely yummy") and she appeared to have evidence that it might just work. Brace yourself for Marmite Vindaloo.

Cheryl's fellow travellers had less success. Nick and Giles English, who sound like cartoon characters, had given up their City jobs to start a watch company, selling wildly expensive wrist trinkets to the kind of hedge-fund hoorays who can drop £7,000 on impressing their mates. Understandably, perhaps, they thought that the booming tiger economy of India, heaving with fresh-minted millionaires, was the perfect place to expand their turnover. Sadly, they'd reckoned without import taxes of 58 per cent, a fixed disinclination to pay the standard retail price and an affection for gold. Nick and Giles, who make their watches out of bits of old Spitfire and market them on their ability to withstand g-forces, looked a bit crestfallen. "It's not a back-of-the fag-packet calculation anymore," said Nick (or Giles), apparently unabashed that they should have launched an overseas export drive on such a flimsy basis in the first place.

But Theo reserved the Dragons' Den head-shaking and tutting for the men from Regenatec, a British company that markets a way to convert standard diesel engines to run on bio-fuel. It's a terrific idea, but is only likely to work if they can undercut state-subsidised fuels, and get the terrifying local pressing plants to produce a consistent product. Mike, who'd come up with the technology and already had his firm "rescued" once, seemed to have a touching faith in the willingness of premium customers to pay over the odds for their fuel because it was greener than the alternatives. You nearly went bust with that strategy, Theo reminded him. "But the business would have gone bust a darn sight quicker had I not had premium customers," replied Mike triumphantly. Yes, there might have been a gaping hole in the hull but just look at the size of my bailers. Theo sucked his oversized teeth and looked disapproving. He's not bad incidentally, despite an odd kind of diction that suggests that he's just had dental anaesthetic injected into both gums, and the series he presents offers a refreshingly novel kind of travel programme, in which you see a culture at work, rather than just pandering to Western leisure.

For all I know, Tom Cunliffe lives in an new-build executive estate in Chingford and does all his seafaring in his imagination, but he looks authentically salty in his pea-coat and neckerchief and The Boats That Built Britain has a genuinely appealing tang of hobbyist passion. This week, Cunliffe was sailing on a square-rigger – the ship that laid the foundations for the British empire – and to say he was excited about it would be an understatement. To see a square-rigger "bearing down on you with a bone in her teeth and her topsails bellying out to the wind", he said, "is one of the great thrills this world has to offer". He then demonstrated just how much hard labour used to be packed into what has faded into a blithe cliché of departure – "setting sail". To us landlubbers, it sounds like just one action, but it's actually hundreds and almost all of them leave you with blisters on your hands.

When did it become the norm to start programmes off with a long explanatory overture that, maddeningly, never changes? The Story of Science – Power, Proof and Passion is actually quite a good beginner's guide to the scientific enlightenment, but to get to the goods you have to sit there for two minutes and 10 seconds while Michael Mosley sets out his stall, exactly as he did last week and the week before that. How many viewers, I wonder, lose patience, and move on to a different stall altogether?