When the train is full to overflowing, I send off a letter to the Department for Transport. Here's one of their replies:

27 January 2012 Dear Mr Locke, Thank you for your email of 10 December 2011 to General Enquiries at the DfT about your journeys from Trowbridge to Bath Spa on First Great Western trains. First; I apologies for the length of time it has taken to reply to you. I am also _sorry to hear about your unpleasant travel experience. In your letter you highlighted your concerns about overcrowding on FGW trains when you travel in them from Trowbridge to Bath Spa. I recognise that this does not address your specific complaint, however, you may never the less be interested to hear that the Government has looked afresh at earlier plans to increase rail capacity by acquiring new trains. The Government has a programme under which additional rolling stock to address over crowding is funded. This programme has led to new rolling stock being ordered, and allowed other rolling stock to be made available to train operators elsewhere. The Department has recently concluded HLOS deals with FGW which will provide additional rolling stock to strengthen the busiest local regional services including the Bristol area. Correspondence from the public does form an important part of our understanding of how rail franchises are performing and I am therefore grateful that you have taken the time to bring your concerns to our attention. Yours sincerely,