The Czech constitutional court has cleared the Lisbon Treaty, as my colleague in Warsaw reports here.

Klaus – the last man standing between David Cameron and Lisbon’s ratification – could now sign the treaty within a month. Now it’s just a waiting game for Cameron to drop his promised referendum on Lisbon, a pledge which was always going to be difficult to maintain.

Jean Eaglesham writes here that: “David Cameron is poised to rule out a referendum on the Lisbon Treaty….an announcement would come ‘very soon’.”

David Cameron faces a horrible decision if the Lisbon treaty comes into force. A quick glance at the policy options makes it obvious why he doesn’t want to explain what he would do. Playing hardball runs the risk of wasting the first year (term?) of a Tory government in a fruitless European battle. The pragmatic route, however, will never satisfy his party. So what to do? Here’s a quick Q&A.

How can Cameron change the Lisbon treaty? Merely to start a formal renegotiation, Cameron would need to propose an Intergovernmental Conference and win the support of 14 countries – a simple majority of member states.

What, 14 countries? That seems like a lot. Yes. And negotiating Lisbon Mark-2 is about as appealing to other European leaders as watching test match cricket.

But many governments do want to repatriate powers, don’t they? Yes. But those demands were all raised during Lisbon talks. Remember, every change to a treaty clause requires unanimous consent. So you need 14 countries to start a negotiation and 27 countries to end it. It just takes one country to dig their heels in and it’s game over. Cameron could be making lots of trips to Riga, Sofia and Talin.

Umm…sounds hard. What could Cameron do to persuade them? He could call a referendum on Europe, either before or after trying to renegotiate the treaty. That would give him a mandate for talks – if the vote went the right way, on a question that was relevant.

But the rest of Europe could still block him. What then? Sabotage. Cameron could withhold Britain’s budget contribution, leave an empty chair at meetings or hold up the EU’s next treaty, which would be needed to accept Croatia or Iceland as members.

Hard ball! Would they listen? Once they stopped yelling? Possibly. But, at this stage, we’d be months into an unholy row. And every European diplomat would know that Cameron had invested a big chunk of his political capital into emerging victorious. They could offer him a face saving deal – but the ransom would be high.

Ouch. Is there an easier way? The pragmatic approach is for Cameron to threaten a referendum, while seeking some kind of concession that would allow him to declare victory.

What could that be? Well, he could ask for a “declaration of subsidiarity” on social policy for instance, which would make absolutely clear that any new rules would be primarily determined by Britain. Victory! The “declaration” would only be passed, of course, because it would have absolutely no legal force. No other countries would care. Peace in our time!

Wait a minute! That won’t meet the Tory manifesto commitment to opt-out of the social chapter? No. It would be purely symbolic. But be realistic. Restoring the social chapter opt-out is harder than it sounds. The chapter no longer exists; it is integrated into the Lisbon treaty. So Cameron would have to propose a fresh treaty negotiation, win the support of 14 countries to start, and then 27 countries to finish. So back to square one.