But as pointed out the 158/159s aren’t spare!
Not ‘spare’ as such, but in BR days any suitable stock that wasn’t actually in use could be pressed into service where needed.
For example, when I was a youngster the Cardiff to Portsmouth trains were rostered for a Class 35 and 7 Mk1s, (from the portsmouth end, BSK, SK, SK, RMB, SO, CK, BSK).
However, if the intended stock or loco wasn’t available, wherever possible something would be cobbled together, a motley collection of MK1s and locomotive substitutions including Class 31s, 33s, 37s and 47s. To a certain extent, when the scheduled stock wasn’t available, most available stock would become ‘common user’ to avoid inconveniencing the passengers.
It was the same on most routes, I can remember travelling on a hastily-organised substitute set of MK1s and a Class 73 stepping-in for a 4-REP and TC formation at Bournemouth Central one summer afternoon. It was a few minutes late and we were missing a buffet car, but it was much better than expecting everyone to be inconvenienced by trying to squeeze onto the following service.
Lastly, I remember seriously heavy snow on the mid/late 1980s resulting in diesel loco haulage of 4-EPBs on suburban services on the Eastern section - with even Class 56s drafted in! Services were disrupted, but we still got home. Today, a couple of flakes and the service would be suspended.
The fragmentation of the network has stripped the railway of the capacity to be flexible and innovative when things go wrong. That’s why customers are fed up, seeing perfectly good assets sitting around while they pay ridiculous amounts of money for a non-existent service.
Back to the topic of this thread, something needs to be done soon as it is now beyond a joke.