Because 1W32 15:50 PAD^» (Paddington (London) - next trains) MIM terminated at Oxford. For the third day in succession. This service's profile on OnTimeTrains is abysmal:

(Great Western - used as an abbreviation for the area / lines under the Great Western franchise, as opposed to FGW which includes "First", the company operating them too. For tickets - about);dayOfWeekRange=Weekdays;dateRange=12W" target="_blank">https://www.ontimetrains.co.uk/journeys/PAD/MIM/15:50/17:26/GW;dayOfWeekRange=Weekdays;dateRange=12W

Presumably the 'broken down train' referred to above isn't the HST^▸ (High Speed Train) on this service since the return (from Oxford) is still slated to run?

Not sure if this was to have been an IET^▸ (Intercity Express Train) or HST^▸ (High Speed Train)

I was on the 05:28 HFD^» (Hereford - next trains):PAD^» (Paddington (London) - next trains) - standing everywhere past Reading (and possibly past Oxford, though it was at Reading I saw the overflow. Seat reservations in the bin as well - didn't affect me, but irksome for pax who've got one then to find it's worth nowt.

HST^▸ (High Speed Train) – not sure what the fault is/was

Likely due to 16:22 1W33 PAD^» (Paddington (London) - next trains):GMV giving up the ghost at Oxford:

The 05:28 HFD^» (Hereford - next trains):PAD^» (Paddington (London) - next trains) started this morning from WOS^» (Worcester Shrub Hill - next trains), and is currently around 20 minutes late and running direct from MIM to OXF^» (Oxford - next trains) to try to make up some time. It's an HST^▸ (High Speed Train) rather than IET9.

The 16:22 PAD^» (Paddington (London) - next trains):GMV (which I'm guessing forms the above) didn't make it beyond Reading:

Only minutes before departure time - train was at the platform at PAD^» (Paddington (London) - next trains).

I was on the 05:28, and remarkably it went from 15' late at M-in-M to 2' late at Paddington, pickup 12' by virtue of the 'express' run between M-in-M and Oxford.

I must have missed the electrification between Worcester's two stations …

On a more serious note: any idea what this relates to?

Thanks! Yes, it's been my twice-weekly ride home for the last six months or so (though through choice not today, as luck would have it) and it's generally been spot on

RTT^» (Real Time Trains - website) lists as "This service was cancelled throughout due to a mishap (MY)." Note sure what qualifies as 'a mishap' ...

I was wondering that. I saw that the service was 35 minutes late leaving Hereford - could the diversion have been to avoid fouling up other services on the single-track sections of the line?