Rail bosses have reassured commuters power lines are being upgraded to prevent a repeat on this week’s hot weather meltdown.

Commuters criticised National Express East Anglia and Network Rail after dozens of trains were cancelled or delayed after soaring temperatures on Monday caused overhead power lines to sag.

As customers demanded answers, rail companies countered by saying a £200million programme was already well under way, aimed at overcoming such problems.

A Network Rail spokesman said: “Whether people are unaware of it or have simply forgotten, we started this work in 2009 and it will be going on until 2014. When the lines are closed and routes are altered on bank holidays or at weekends, that’s because we are doing our best to bring our infrastructure into the 21st century.”

Andrew Chivers, managing director of National Express East Anglia, promised: “The new system will be much more reliable and will allow for adjustment of the tension of the wires to compensate for extreme temperatures.”

A collapsed power line on the Liverpool Street to Southend Victoria line caused havoc on Monday evening, as busy trains were cancelled and sweletering commuters were shifted on to buses in Shenfield for the trip home by road.

The chaos followed problems with the 50 to 60-year-old overhead lines, which forced speed limits on the line earlier in the day. There were delays, too, on the c2c line after a suspected theft of cables at Upminster.

Rail companies have offered compensation to travellers delayed by more than 30 minutes on Monday. However, the offer fell on largely deaf ears as angry commuters, many of whom got home two hours late, demanded action.

Rochford man Tommy Rodgers, who runs the website, www.trainrage.com said: “The hot weather was yet another laughable excuse for our decaying rail network, for which commuters already pay over the odds.

“National Express East Anglia struggles to run trains at the best of times and Monday’s incompetence was yet another kick in the teeth for commuters.”