Didcot is only xx13 / xx43 off-peak. At other times, the slower workings are still timed in front of a Heathrow service.
Yes but what I meant was the Didcot services running semi-fast has nothing to do with Heathrow Express at a core level (sure you still have to plan the service approriately for margins, recoccupancy, headways etc.) as that isn't something on the cards yet.
GWR would definitely find a use for an additional 4 fast paths out of Paddington every hour
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London Paddington.
Sounds correct because of the Heathrow premium.