Thanks for these figures. The original point was that it is not longer possible to give passengers the amount of space they would normally have had in the 1960s. So the comparison was with the IEP as proposed, with a conventional train with all seating in facing bays. That means a longer train, as the calculation showed. It may or may not be a problem, though probably not one that SDO would not solve.
Adopting IEP seating density, a 23 metre vehicle would carry at least 80 standard class passengers, perhaps 84. At a conservative estimate, the 11 car conventional train would then have seating for 640 standard class, plus, say, 100 first class ie 740 seats.
The real reason for the cramming of seats is presumably due to the cost of the trains. The 9 car IEP has 625 seats. The cost of the trains is given at around £2.6 million. That works out at £37,000 per seat.
An alternative train might have had 11 trailers, say £1 million each, plus an off-the-peg locomotive like the proposed UK version of the TRAXX. Presumably Siemens could offer a UK version of its Vectron if there was a call. These seem to be around £3 million at the moment, so a complete train would have been about £14 million. That works out at just under £21,000 per seat with 72 seat in standard class and under £20,000 with 76 seats in standard class ie about one-third unidirectional, in line with passengers' preferences. If the programme had also included some mark 3 refurbishment, the average cost per seat would have been brought down further. Of course mark 3 stock cannot go on for ever but £500,000 per vehicle would have paid for a lot of upgrading and life extension.
If you want to know what the vehicle would look like,
there is this prototype here, one of the vehicles in the BREL International set. Based on the mark 3, this was a 23 metre vehicle divided into 9 bays of, probably 1.90 metres, compared to the 8 x 2.1 metre bay mark 3, thus there was the possibility of arranging all seats in facing bays aligned with windows.
