THE company which built the collapsed railway tunnel at Gerrards Cross is exploring "every single option" to find out what went wrong.

Richard Neall, chief executive of Jackson Civil Engineering, said colleagues from around the world were trying to establish what caused a 30-metre section to give way without warning.

"We are uncertain at this stage," he said. "The difficulty is knowing how long it will be before we find out what caused the collapse."

"We are taking the view that we must analyse every single option, the architecture, the design the workmanship, everything. This is not a five minute job."

Mr Neall said he appreciated the issue of compensation for Chiltern Railways and passengers had been raised.

"We will face that head on along with everything else," he said.

He confirmed after initial safety concerns, workmen were able to examine the inside of the tunnel to check for further damage.

Mr Neall added: "On a visual basis it would appear that the other parts of the tunnel are fine."

According to Mr Neall, suggestions from experts that heavy rainfall may have been the cause of the collapse appeared inaccurate.

"Any structure in this country needs to be fully designed to cope with the weather conditions," he said.

But he would not be drawn on what effect the collapse would have on Tesco.

"It's too early to say," he said. "The priority is to run a clean-up operation."