The last time there was a general service reduction of rail services was in the recession of the early 90s, before the privatisation plan took hold, when a 10% cut was imposed (while large sums were being spent on Channel Tunnel routes and services).
BR did reduce service frequency, but it also rationalised its rolling stock by ditching much elderly and non-standard stock, and rolled out more DOO.
It was when sleeper services were drastically cut, along with portion working which was common previously on some routes.
Once the cuts were achieved, there was then 30 years of expansion, even through recessions, as the 5-year CP and 7-15 year franchise contracts protected the status quo, unlike in other government agencies.
None of that applies today, with short-term contracts being the order of the day, putting more power in DfT hands.
NR also has its enhancement projects authorised separately, not as part of the CP settlement.