The article claims that the UK is currently bound by decisions of the European Court of Human Rights (ECtHR), such that the latter can overturn decisions of the former's national courts. That claim is incorrect: the relevant legislation is Human Rights Act 1998, section 2 <http://www.legislation.gov.uk/ukpga/1998/42/section/2> of which only requires national courts to "take into account" the ECtHR judgments—i.e. UK courts are persuaded by, but not bound to follow, them.
Thus, whilst signatories to the European Convention on Human Rights (ECHR) have international treaty obligations to abide by decisions of the ECtHR, there are no sanctions available for states who ignore them! The matter gets referred to the Committee of Ministers, who could ultimately kick a state out of the Council of Europe, but that has never yet happened (and there is a very long list of ECtHR judgments that have been egregiously ignored by signatory states).
It's true the EU does not require its member states to themselves sign the ECHR, but it is important to note that the EU has itself done so: <http://hub.coe.int/what-we-do/human-rights/eu-accession-to-the-convention>. Thus any case that can be brought before the ECJ (the supreme court of the EU, whose decisions *are* binding on the national courts of member states—a requirement of EU membership) will almost certainly consider ECtHR decisions to be persuasive to the point of being bound thereby. Thus if the UK seceded from the ECHR, or even the CoE generally, it would still find itself bound by such rulings on a great many subjects unless it also secedes from the EU. And that's not to forget the legal basis of the Charter of Fundamental Rights of the European Union (the UK's supposed "opt-out" arguably having little practical effect).
Furthermore the UK (and EU) are also signatory to other international human rights treaties, such as the Universal Declaration of Human Rights—violations of which can be petitioned before the UN.
So it is awfully unclear what the Conservatives actually mean by all this political posturing and headline-grabbing electioneering, since the reality is that there is very little that the UK can do without renouncing a great many international treaties (which would probably necessitate it seceding from a number of significant intergovernmental institutions). It's a pipe dream, but not a very realistic one.
There's a ton of excellent resources for those who would like to read more, but two I'd highly recommend are:
A 2013 interview in The Guardian with Lord Neuberger (President of the Suprement Court) <http://www.theguardian.com/law/2013/mar/05/lord-neuberger-deportation-terror-suspects>
A House of Commons briefing paper "European Court of Human Rights rulings: are there options for governments?" <http://www.parliament.uk/briefing-papers/SN05941.pdf>