The UK remains a sovereign country - all it would take is an act of Parliament declaring that the Bill of Rights would outrank any other jurisdiction and that we have our own laws. Not that we disagree with the aims of the ECHR, it's just that its application to English law is causing too many problems and leading to a sense of injustice.
But Dominic Grieve, perhaps the strongest supporter of the ECHR in the front bench, is adamant that the Bill of Rights would stay junior (and, ergo, irrelevant). I can understand why Cameron may think he has enough battles, but ducking this would would be a grave error. All his plans on controlling immigration, fighting terrorism, or toughening criminal sentences will be subject to the ECHR. It's the biggest mistake in politics to judge a policy or law by its intentions rather than its outcomes. The myriad unintended consequences of the ECHR (and the Human Rights Act) are well-understood by the British public but not understood by the political elite who still seem dazzled by its lofty ideals.
If Cameron misses the chance of making his Bill of Rights senior to the ECHR, then when he gets to No.10 he'll find out that half of the tools he'll need to transform Britain will be locked up with the key in Strasbourg.