However, it would help to make realistic suggestions. Frank may not have spotted that our rail lines are narrow gauge, so double-decker trains would be dangerously unstable on these and in any case, most of the bridges are way too low.
In addition, with the island platform layout on most of our stations, lengthening those platforms would also require rail re-alignment, so it would be a massive capital expense and a very long program of works to achieve it before the longer trains ever begin to run.
The simple and blindingly obvious solution is not bigger trains but more trains. Here on the Midland line they actually cut the frequency of morning rush-hour trains. There used to be nine city-bound trains through Bayswater between 7am and 8am, and a couple of years ago the clever people at Transperth cut it to six trains, many of which are totally full by the time they get here.
Then in the evening, the trains all go home to bed. A half-hour service on a main line in a big city is pathetic.
We also need proper feeder services to our stations. The volume of commuter car parking in the streets around those has become ridiculous.
Public transport is the only 21st century solution, not more roads.