The Richard Rogers Partnership, Pascall and Watson and BAA are all adamant that the scheme - which was first drawn up in the 1980s - has enough inherent flexibility to be left largely as it is.
The three have denied rumours of plans for an emergency meeting of the design team to assess any changes needed to the security provision in the new terminal.
A spokesman for Richard Rogers said the designs were 'inherently flexible' enough to deal with any changes to security that are required as the terror threat evolves over time.
Pascall and Watson's T5 director Steve West agreed. 'We have very strict security measures in place already,' he said.
'Security is under review all the time, but last week's alert will make no real difference to that,' he added.
And an over-worked and hassled press officer at BAA also towed this official line. 'We are confident that the designs as they are have the flexibility to meet any changes to the security provision,' she said.
However another airport design expert, GMW's Gunter Pueschel, said the events of last week would have consequences for everyone involved in the industry.
'It is inevitable that this kind of alert will have some consequences for Terminal 5,' Pueschel said. 'They will have to look at things like the provision of space for the increased number of scanning machines.'