Last week I visited Portsmouth for the first time in years. One of the historical homes of Britain's navy down the centuries, today it feels more like a quiet backwater with just continental ferries to disturb the peace. On my last visit, shortly after the Task Force had returned from the Falkland Islands, the harbour was dominated by the unmistakeable sea-grey of the Royal Navy. Today, to underscore how much things have changed, only a couple of smokestacks are visible. Indeed, there is even a rumour circulating in the local press that the Royal Navy's dockyards risk closure as the senior service faces up to the reality of Treasury cut-backs.

The symbolism seems even starker as it emerged this weekend that David Cameron is now seriously mooting the possibility of a referendum on our EU membership, while his former Defence Secretary Liam Fox, the darling of Tory Eurosceptics everywhere, is today demanding a renegotiation of our membership or an out-and-out withdrawal from the EU if that fails. The only thing to be said for Dr Fox's arguments is that they are clear and uncompromising. This is in stark contrast to the pronouncements of his former boss on what exactly we, the British electorate, would be asked in such a referendum. These, to quote an old teacher of mine, are "clear as mud".

The restive Tory Europhobes have a high-profile champion in Liam Fox - a heavy-weight whose sound-bites attract the attention they crave in their zealous pursuit of "an escape from Europe". Indeed, so focused are they on the purported evils of Brussels, they seem blissfully unaware of the logical conclusion of their policy. This would be to lead us into a very unsplendid isolation, rendering us increasingly irrelevant on the international stage, unable to defend our interests in probably the most turbulent period in international relations for nearly a century.

For let us be clear on what is being suggested here. Siren words about renegotiation are just that. If we honestly believe that as just one of 27, we can turn to our EU partners and demand to renegotiate the terms of our membership on the basis of some "à la carte" policy pick'n'mix, we are sorely mistaken. The suggestion that we will leave if we do not get what we want will be met with regrets but little more. In essence, we are asking our partners to let us have our cake and eat it - to participate, but only on our own terms. If we do that, why should France or Germany, or Italy or Poland, or any of the others not do likewise? Every member state has things it likes and dislikes about the EU - but it comes as a package, otherwise the whole entity unravels. I have been told repeatedly by diplomats involved in representing our interests in Brussels that the point is to be inside the room seeking to influence the argument. On the outside, you can do nothing.

Of course, most anti-European Tories understand this: they know that the choice between renegotiation and departure is really no choice at all. They are itching to be able to withdraw from the EU, convinced that by doing so Britain will somehow regain all its lost influence. But in this is a dangerous illusion. In relative decline for at least the last half-century, Britain's power and influence today rests on its many multilateral commitments. But in particular, it is our memberships of the UN (especially the Security Council), NATO and the EU which provide the basis of our influence on the international stage today.

We are able to fight our corner - punch above our weight, in fact - because of our place in the EU, not in spite of it. Our close relationship with the US relies on our being a key decision-maker in Brussels - so how much attention will Washington pay us if we choose to retreat to the periphery? And while politicians may deny any link between the two, in the longer term departure from the EU would call into question our ability to remain on the Security Council. Part of the argument we make for our continuing membership is the sense of legitimacy arising from our commitment to multilateralism. Outside the EU, how long could we withstand calls to give up our seat in the face of serious and concerted efforts to reform this body?

This, then, is the price we would pay for what the Tory Right likes to present as the reclaiming of Britain's sovereignty. The reality is that their policy is blinkered and insular. At a time when we face ever increasing austerity at home, Dr Fox and his allies would now like us to face isolation, irrelevance and weakness abroad. The Prime Minister's response? Prevarication.

So much for the national interest.

(Originally posted 2 July 2012 on Yet Another Politics Junkie)

Follow Nicholas Wright on Twitter: www.twitter.com/NickWrightYAPJ