It would be very easy to write the franchise agreement in a way which bans station skipping.
The train operator would then have to respond in one or more of several ways:
- Terminate trains short instead of skip stopping
- Cancel trains instead of skip stopping
- Increase turn around times to reduce need for skip stopping
- Reduce stock/crew utilisation to allow more "spare" stock and crew at termini to reduce need for skip stopping
The problem is that options 1 and 2 are actually worse for passengers than skip stopping (which is why the operator currently does skip stopping) while options 3 and 4 would cost extra money to the government in subsidy (so we need to have a conversation about how bad skip stopping is and what we are willing to pay to have it not happen).
Investment in more redoubling, infrastructure reliability etc can all help reduce the requirement for skip stopping as well but ultimately once services are delayed and out of position the only options to get back to normal service are skip stopping or cancellations. Making skip stopping the political flavour of the day is just going to lead to Scotrail having to cancel more services instead.