From National Rail:
"The emergency services are dealing with an incident between Swindon and Didcot Parkway. So they can safely carry out their work, all lines are closed.
As a result, trains may be cancelled, delayed by up to 60 minutes or revised.
Major disruption is expected until 18:00.
Customer advice:
A very limited rail replacement services is in operation between Bristol Temple Meads / Swindon and Didcot Parkway.
You can use your ticket on Stagecoach Bus route 55 between Swindon and Chippenham, and route S6 between Swindon and Oxford at no extra cost.
You may use your ticket on the following services:
CrossCountry via any reasonable route
Elizabeth line via any reasonable route
Chiltern Railways between Oxford and London Marylebone"

Worryingly this is about the 3rd such incident being dealt with by Emergency Services between Swindon and Didcot in the last week or so.

Yep, I think it was the third one in about a fortnight....sad times