If there was no actual accident it may have only made into the internal safety reports etc,
so I'd suggest it might show up in a search of
RSSB▸ 's various archived reports for the time:
http://www.rssb.co.uk/SiteCollectionDocuments/pdf/aspr200102%20apps.pdf (Annual Safety Performance Report)
This is probably it:
13.10.01 Bedwyn - Gt Western - Thames Trains
Empty
DMU▸ derailed in siding following
SPAD▸ ;
obstructed running line
Just in case their search engine is under reporting results for Bedwyn, there's a list of documents here to trawl through manually:
http://www.rssb.co.uk/Pages/Published%20Documents.aspx I also had a quick look at the 'Railways Archive' website,
http://www.railwaysarchive.co.uk/index.php but that doesn't seem to hold anything that I can find easily - could the incident be logged under somewhere else than Bedwyn?
Hope that helps - even if only a start
PS - added
HSE▸ to a Google search for Oct 01 and found this:
The HSE said that in the October 2001 case, the Thames driver, who was taking the train from sidings into Bedwyn station, had failed to check the signal and that the signal "was not as clearly visible as it should have been due to encroaching vegetation".
It added that the Great Western driver had brought his train to a halt some 1,500 yards short of the derailment.
The HSE's Railway Inspectorate has ordered Thames to review the fitness and and competence of the driver involved and has required Railtrack to make sure that the signal is more easily seen.
http://www.telegraph.co.uk/news/1396340/Spads-hit-record-low-in-April.htmlPaul