Signal failure delays commuters travelling west of London
Commuters travelling on First Great Western services have been experiencing delays of up to 90 minutes due to signal failures.
Lines between Maidenhead and Slough were affected due to Network Rail signalling problems earlier.
First Great Western said services running through these stations may be cancelled, delayed or revised at short notice.
A company spokesman said normal services should resume on Thursday.
He said between four and six trains were on the line at the time the problems hit, with hundreds of passengers potentially affected.
'Chaos on railway'
Some passengers described their experiences on social media. Those on delayed trains reported being stuck on hot trains for 90 minutes and more.
One, Guy Rigby , said on Twitter: "First Great Western Delays becoming institutionalised. Chaos on the railway tonight! Delays of 90 mins on trains at circa 40 degrees C!"
Others described confusion at Paddington as passengers waited to board a train.
A spokesman for First Great Western said: "We appreciated that the heat would have been an issue for those passengers. However, the trains have been fitted with air conditioning so hopefully that would have helped.
"We would like to apologise to those who have been inconvenienced."
The First Great Western website said that South West Trains services were carrying passengers between Reading and London Waterloo in both directions until further notice.
Transport for London services are carrying First Great Western passengers via any reasonable route "until further notice".
Arrangements have been made for First Great Western rail tickets to be accepted for these journeys.
A spokesman for Network Rail advised anyone planning to travel to check National Rail Enquiries for updates.
There were also problems on the London Underground's Jubilee Line because of signal failure at Neasden. There are still minor delays on the line.