On the final day of the committee, Timothy Mould QC - lead counsel for the Department for Transport - said: “I showed the committee an exhibit of a cross section which gave a dimension between the running tunnel closest to her property and the surface of the ground.
“We have, I regret to say, discovered that that dimension as shown on that exhibit was incorrect, and it exaggerated the distance between the running tunnel and the surface of the ground.”
Mrs Brennan feels that petitioners and campaigners have been misled for three years after the revelations.
She said: “In 2012, they announced that a tunnel would cut through the Ruislip stretch at about 30m-deep and maps showed this. 22 months later we received maps again so it's been constantly reinforced all the way through that our tunnel not changed.
“I'm worried about how deep the tunnel really is and why they haven't told us until now. They would have let me petition based on that wrong map and I wouldn't have known.
“There's hundreds of residents who now know about the tunnel depth thanks to us and they're all panicking. It's a horrible feeling.”
'Feeling of distrust'
Mr Hurd said: “You have heard from other MPs, about failings in the way that HS2 have engaged with residents... it does leave us with a problem, which is a very low residue of trust as we go forward."
Speaking later in the hearing, Mr Johnson, said: “I have to say that the feeling of distrust has been intensified just in the last 24 hours by this revelation that the existing proposed tunnel will turn out to be only half as deep, as was first understood to be the case.
“It's a great pity and I hope that matter can be speedily resolved and a proper understanding of what exactly this tunnel will deliver by way of protection to those residents can be reached.”
Lottie Jones, who also submitted an individual petition about her property on Almond Close, spoke out and wants to “push the apology further”.
She said: “They only apologised to the four petitioners but, quite clearly, it affects all the residents of Ruislip who back onto the tunnel, of which there are hundreds. Their apology doesn't go far enough and doesn't allow for how many more people are affected.
“Our argument now is that they've misled us. If their engineers couldn't get that basic measurement right, how can we possibly believe their predictions for how our properties are going to be affected?”
Alastair Cowan, a spokesman for HS2 Ltd, said: “It has come to our attention that plans provided to three properties in Ruislip incorrectly show the HS2 tunnels as between 5m and 15m deeper than they actually will be. The plans have now been corrected and we have apologised for the mistake.”
Petitioners now wait to hear from HS2 to meet with them and discuss what will happen next.