It is something of a paradox that both sides of the argument in the EU debate are relying heavily on the thorny issue of border controls to make their case.

For Brexit supporters, it is crystal clear: unless and until the UK can wrest control of our borders from Brussels, the influx of migrants will continue largely unabated.

For supporters of staying in, it is also clear: it is the existence of joint agreements with our partners - in this case the Treaty of Touquet - that ensures the UK’s borders are safeguarded against such an influx.

Can both be right? Confusing as it is, the two sides have a point.

The arrangements agreed with the French in 2003 that resulted in the Treaty of Touquet means that our border officials operate across the Channel.

In so doing, they are in a position of being able to halt illegal migrants getting to the UK, where they could rightly claim asylum.

But Brexit supporters counter that this is misleading because the Treaty of Touquet is simply a bi-lateral deal with France, not with the other member states.

The treaty came about as a result of the consequences of the first migrant camp at Sangatte and the concerns the UK government had about the French authorities waving migrants through.

So, inevitably, we have seen an early skirmish between the pro and anti camps, the latter accusing the PM of scaremongering.

It is certainly an indication that the Prime Minister is prepared to go on the offensive on the issue. He is planting the idea in people's minds in the hope that they may consider the option of staying in rather than getting out.

Invoking the prospect of refugee camps in the Garden of England - and suggesting that it would expose the country to security threats - is a calculated move.

It is what footballers call getting your retaliation in first - probably a good idea when you have the likes of Nigel Farage nipping at your heels.

The key question is whether linking the two issues of national security with the jungle camps will get any traction with undecided voters.