I woulnd't count myself as an expert on the rules, but don't the national conditions require that you buy not just a ticket but a a ticket for your journey before boarding. You could interpret this to mean that you need a ticket for your entire intended journey before you board. ...
Good point - National Condition of Carriage No. 2:
Before you travel you must have a ticket or other authority to travel which is valid for the train(s) you intend to use and for the journey you intend to make.
So if I
intend to travel from London to Newport, using my London to Oxford seascon as far as Didcot, I must purchase the Didcot to Newport leg before I leave London to be within the rules.
There are some odd-looking side effects (new example)...
If I get on the Bristol train intending to change at Didcot to go to Oxford, but get a call from my partner telling me that she's been held up and can't be in Oxford that evening - come home to Melksham,
it is legitimate for me to buy the Didcot to Chippenham section on the train, since I started with a ticket for my intended journey. However, if I receive her phone call BEFORE I board the train, I need to purchase the upgrade before I join the train and (since it says "the journey" in the conditions), I technically need my Chippenham to Melksham bus ticket too ((in a realistic scenario, I wouldn't have been lucky enough to be leaving London on the single daily train that actually has an onward conenction to Melksham!))
The rules are not worded as clearly as I would have written them. Rule 2 suggests that the requirement for a valid ticket for your intended journey is a one-off requirement which must be met at the start of your journey rather than an on-going requirement throughout your journey ("
before you travel" not during your travels).
However, there are other rules that require you to have a valid ticket throughout your actual journey (If rule 2 was the only rule you could meet the requirements of the NCoC at Paddington and then throw your tickets away before boarding your train!)
The issue of whether they can sell you a ticket on the train or not is a matter of
FGW▸ policy and/or staff descretion not a matter for the NCoC. (
TOCs▸ are obligied to sell you tickets at stations and if your ticket isn't availalable you can't be punished for boarding without one. TOCs do not have an obligation to sell you tickets on a train - it is up to them what range they sell on a train at least if you have already had the opertunity to buy before you boarded)
To be on the safe-side you would need to buy your Didcot-Chippenham ticket at Paddington (or get off at Didcott and buy it) but if you ask nicely and before Didcot you might get shown some leniency.... and if you didn't you could get off at Didcot and escape a penalty.
I don't think you would need your bus ticket to Melksham before you board. i would construe "journey" to be limited to your national rail journey because the NCoC are not applicable to your bus journey (unless it is a rail replacement bus). It would be very odd if the NCoC were construed to regulate journeys not regulated by the NCoC.
As an aside, the language "for your journey" is also in the condition that requires you to show a valid ticket for inspection. I take this to mean that when you are travelling on a multi-ticket journey you should strictly offer all your tickets to the guard for gripping (or at least all of those applicable to his train) when asked "tickets please" rather than just the ticket covering the part of the journey you are currently on.