This was the response:
Thank you for your email of 2 March about the EU Constitutional Treaty. You asked for the British Government's position on the effect of the Treaty on national sovereignty.Anyone who wants to have another go can e-mail the FCO, using this address. However, banging your head against the wall might get a better result.
The British Government does not agree that the EU Constitutional Treaty threatens Britain's sovereignty. The Treaty confirms that the EU is a union of nation states which only has the powers given to it by those states. It establishes clearly where the EU can and cannot act, and ensures that the most important decisions, such as those on tax, social security, foreign policy and defence, can still only be taken if all Member States agree. Britain also retains the right to opt out of measures affecting our laws on asylum and immigration. This is clearly not a Treaty which reduces Britain's power as a nation.