Ah yes, Theresa May's famous red lines
I don't know if anyone else has seen this, The Brexit Witness Archive. It has a collection of interviews with key people from both sides of the Brexit divide.
Philip Hammond on Theresa May is very interesting. Those 'red lines' were set at her first speech on Brexit. This is what Hammond has to say (but the whole lot is worth reading)
I did ask her about Brexit, and she said to me, ‘Brexit means Brexit.’ That was it. That was the only discussion we had about it.
Look, what happened, I was completely stunned by the speech that she made at the Conservative Party Conference in October 2016. I hadn’t seen the relevant part of it in advance. I’d had no input to the speech. Nick Timothy kept me completely away from it. I did see some text on the economy the day before, but I had no idea that she was going to describe Brexit in the hardest possible terms.
I was absolutely horrified by what I was hearing.
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My assessment of Theresa May’s Prime Ministership, in terms of Brexit, is that she dug a 20-foot-deep hole in October 2016 in making that speech and, from that moment onwards, cupful by cupful of earth at a time, was trying to fill it in a bit so that she wasn’t in such a deep mess. Every speech she made on Europe since then was rowing back from the original proposition. Lancaster House rowed back from what she implied in the October speech. Florence rowed back a bit further. Mansion House a bit further still. Every time we moved on this, it was to move backwards from the brink.
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It was a disaster on all fronts, a total unmitigated disaster that scarred her Prime Ministership and should have sealed Nick Timothy’s fate, but I think she only realised later how badly that had constrained her ability to deliver any kind of practical Brexit at all.
ukandeu.ac.uk/brexit-witness-archive/philip-hammond/
Expand the section 'The First May Government'