From Steve Peers, a member of one of the SY2E – Remain in the EU groups.
1) The UK cannot be required to join an EU army without consent of the UK government, parliament and public;
2) Treaty amendments require the consent of the UK government and parliament, and (if there’s any transfer of powers) the public;
3) Accession of new Member States requires the consent of the UK government and parliament; it is a long way off for Turkey in particular and if it ever happens, will be subject to long periods of transition for workers to be admitted;
4) The UK has a veto on tax issues; the UK government, parliament, and public would have to consent to dropping it;
5) The UK has an opt-out from EU law on asylum, non-EU migration and criminal law; the UK government and parliament would have to consent to dropping it, and the public would have to agree to join Schengen or the European Public Prosecutor;
6) The UK has an opt-out from the single currency and other related issues, and could only join after the consent of the UK government, parliament and public;
7) The UK has a veto over the basic EU budget revenue and spending rules, including the UK budget rebate; the veto could only be dropped with the consent of the UK government, parliament and public.
Of course, there are many other possible criticisms of the European Union. Some may be valid, and some not. But the argument that the UK government could be forced into any of the measures listed above is quite clearly false and scaremongering.
All of the above possible developments are subject to the control of the UK government, and usually our Parliament and the general public besides.