UPDATE

'Minimal' train services between Slough and Paddington are operating again this afternoon - with two of the four lines closed this morning now restored.

Tomorow looks optimistic, although there is the possibility of a knock-on effect.

A spokesman for Network Rail said 500 metres of overhead electric power lines last night had been damaged, adding: “Engineers have been working round the clock and have managed to clear debris from the damage and restore power so trapped trains that were blocking the line can be moved.

“As a result two lines out of the four that are usually used are now open, meaning a minimal service will be in place for the rest of today between London Paddington and Reading and Heathrow. Passengers should check before they travel.

“Passengers travelling to London can also travel to Waterloo via Reading and Marylebone via Oxford. A rail replacement bus service is currently operating between London Paddington and Heathrow Airport."

“Heathrow Express services have now resumed with departures every 30 minutes and passengers are advised to check the latest service information before they travel at heathrowexpress.com.”

*Apparently the damage to the overhead cables that caused this morning's lines closure was caused by a 'test train' - the term used for a new train being tested before coming into service in case there are any problems.