The code is LF.
Have been examining these diagrams and they are certainly pushing the boundaries of what is acceptable for a passenger service, and on train messaging is going to be absolutely key here to avoid customers doing silly things like trying to open doors.
It's quite remarkable to see for a Class 1 passenger service. In particular, 1S01 appears to have a 9 minute dwell at Milton Keynes - fair enough, not great, but no risks there. It then enjoys a spell in the Beattock Down Passenger Loop for almost 20 minutes and then goes off-pattern and omits a call at Larbert. There's also 15 minutes of allowances just between Preston and Carlisle, which could see the train potentially sitting just outside, or at, Carlisle waiting for a platform if it gets a clear run.
On a hot, busy day with the struggling aircon, that 20 mins in a random loop is going to feel like an eternity, especially if the passengers are already feeling frustrated at the exceptionally extended dwells and stops previous.