This can actually include any service which calls at a station which is unusual for one which also calls at another. The train doesn’t actually have to make any deviations from its route or do anything else unusual, although if it does this also counts.
The 07.04 Bath - Filton AW catches out at least one person a week by going direct from Keynsham - Lawrence Hill - especially if it’s running a few minutes late.
This is absolutely next on my list to go on. The last one I made the effort for was SWR’s 1J66 18:47 Salisbury - Reading, which effectively pretends it wants to be a CrossCountry service at Basingstoke, rather than going to the usual Waterloo. There are quite a few of these in SWR’s Diesel operation, including everything that goes via Westbury.
There are also some on the Portsmouth Direct Line. 2Y13 and 2Y61, the 07:15 and 19:15 departures from London Waterloo call at all stations from Woking to Havant, then continue to Southampton Central. The only SWR services to call at several stations otherwise served by Southern.
Conversely, 3 services in each direction starting with 1G22 07:45 Portsmouth Harbour - London Waterloo are non-stop Guildford - London Waterloo, not calling at Woking.
EMR’s Liverpool Lime Street - Norwich makes several 1 a day calls at various stations along its route throughout the day, including Hunts Cross, Hazel Grove and Dore & Totley.
Also 1D06 06:05 and 1D08 06:35 St Pancras - Nottingham and 1B98 16:12 Nottingham - St Pancras International call additionally at Bedford, the only direct services between Leicester and Bedford all day and the only Diesel calls at Bedford.
ScotRail’s 1C06 17:37 Anderston - Carstairs calls at Glasgow Central low level, Argyle Street, Rutherglen, Uddingston, Bellshill, Wishaw, Carluke and Carstairs. Extremely unusual. I don’t know what to say about it.
Many evening Avanti West Coast services have unusual stopping patterns compared to the daytime. Also LNWR’s daily service to Polesworth.
There are also CrossCountry calls at Brockenhurst few times a day. I’m not sure if they make any others like this.
I’ve just noticed a lot around Newcastle. Those Northern services that find themselves at Middlesbrough with a Class 1 headcode. Either 2 hourly off peak Middlesbrough, Thornaby, Hartlepool, Sunderland and Newcastle only, or early morning 3 trains, Middlesbrough - Carlisle, Saltburn - Carlisle and Saltburn - Newcastle run to Darlington then instead of terminating or continuing to Bishop Auckland, call at Durham, Chester-le-Street and Newcastle, with 156s!