Very interesting chat yesterday with Tadashi Arashima, the President and CEO of Toyota Motor Europe at the launch of the much improved Prius.

The conversation concerned plug-in hybrids, the cars many including me have presumed to hold to the key to achieving medium-term emissions reductions, bridging the gap between current hybrids and high efficiency diesels and the fuel cell cars that may (or may not) spell the future of motoring.

The good news is the Prius plug-in is not far away at all – indeed 500 will have been leased by the end of this year with an unspecified but significant number coming to the UK. So far so good.

The bad news is that Arashima-san is not in a position to say when the car might be generally available on sale because ‘the cost of the technology is considerably greater than we first thought.’

The technology he is talking about are the lithium ion batteries (as already available in the vastly expensive Tesla roadster) the plug-in Prius uses.

And if the largest, canniest and, until recently, most profitable car company in the world with 30 years hybrid experience behind it can’t make the plug-in equation add up, it is fair to wonder who can. Arashima doesn’t doubt they’ll get there in the end, but the fact he cannot yet say when should be cause for concern.