The most exasperating thing about all this is it’s hard to pin who is responsible for the continued shortage of crew across the rail network; particularly on weekends. Is it the train company, the unions, the dft even British Rail?
All I do know is there seems to be little urgency to sort it as it’s being going on for years.
Pritvatisation takes a large part of the blame in my book. Previously drivers were a common resource working for one company. Splitting into myriad different companies is inherently inefficient.
Great Western have a tiny depot in Weymouth so when short of crew a train has to be cancelled. Most of the time South West Railway will have a spare drive who could have covered the work in British Rail days. So a driver or guard are available just not the right one.
When new trains are introduced into an area it means a large part of the workforce for the Train Operating Company need training. Ideally you would recruit extra drivers for 18 months but that is not a realistic option. So you have to rely on overtime working which is fine for most of the year but there inevitable pinch points, such as a bank holiday, when you will not get sufficient volunteers so trains have to be cancelled.
Don't forget Great Western have a huge increase in service in December and the staff have to be trained. Usually for the peak summer season you would stop the training for 6 to 8 weeks. However this is not really an option with a hard deadline of timetable change in December.