Now you might think I'm just making a snarky political point. Obviously the back door metaphor has a different meaning in the two contexts. But there is an important connection here, so please bear with me.
The European Data Protection Supervisor is dead against encryption back doors. By mandating encryption back doors, the UK therefore appears to place itself outside the European circle of trust. The proposed legislation would mean that any UK company or UK-based facility might be subject to an equipment interference warrant (aka back door), and would not be permitted to reveal whether it did or not. Aside from the competitive disadvantage that might follow from this potential vulnerability, UK companies and UK-based services would be challenged to demonstrate compliance with the European Data Protection Regulation, and might therefore be prevented from holding data on any European citizen. There is going to be a single market for data, and we wouldn't have access to it. Another blow for the UK service industry.
So evidently Mrs May is right. Backdoor membership of the EU is not on the table.
Anushka Asthana, No staying in the EU by the back door, says Theresa May (Guardian, 31 August 2016)
Jennifer Baker, Encryption backdoors appear on EU data chief’s ban wishlist (Ars Technica, 25 July 2016)
Lucy Mair, Supreme court strikes down Home Office's back-door changes to immigration rules (Guardian, 18 July 2012)
John Naughton, Theresa May’s surveillance plans should worry us all (Guardian, 12 June 2016)
Iain Thomson, FBI Director wants 'adult conversation' about backdooring encryption (The Register, 31 August 2016)
@TheRegister backdoors are like hookers they do what you pay them for but never have them exclusively!— Frank Koster (@bluegoaindian) September 2, 2016