As is often the case with major EU reforms, the outcome of negotiations on overhauling the CAP is likely to be decided during last-minute political haggling between member states, said Thurston, who is co-founder of farmsubsidy.org.
However, one thing appears certain, he says: the EU is moving towards a partial re-nationalisation of its farm policy after 2013, when the bloc's new long-term budget plans will start kicking in.
Even though the move is likely to be resented by countries currently receiving large amounts of subsidies, Thurston believes they will have no choice.
This is because, towards the middle of the next decade, an unreformed CAP would see traditional large recipient countries like France turning into large contributing countries, he said.
CAP funding, "which used to bring in all this good German money to France," will then start flowing to countries like Poland, he said. With co-financing, the money will at least be staying in France rather than going into Polish farmers' pockets, he added.
For the same reasons, co-financing would also be hugely beneficial in budgetary terms to Germany, he added.
"I think everyone is accepting that the CAP budget is going to be co-financed after 2013," Thurston said.
Indeed, Thurston pointed out that France has already started talking about increasing "national responsibility" within the CAP's so-called "first pillar", which governs direct payments to farmers.
During the 2008 CAP health check, former French Agriculture Minister Michel Barnier negotiated key reform – Article 68 – which allows countries to re-direct EU cash from traditional subsidies to new policies to sustain farming, for example in mountain areas, he remarked.
EU budget reform at heart of CAP debate
The European Commission is due to present on 10 November a 'menu' of options for reforming the CAP. Based on the answers it receives, the EU executive will table a formal proposal around middle of next year. The new regime will start applying as of 2014, together with the reformed EU budget framework for the period 2014-2021.
Seen from an EU budget reform perspective, co-financing the CAP would be a convenient way of freeing up much-needed cash and pleasing those who want to fund other priorities, such as innovation and research, Thurston said.
But he said this could also end up increasing the overall cost of the EU for taxpayers, because the European Parliament is unlikely to accept any reduction of the overall EU budget resulting from CAP co-financing, forcing member states to find fresh money to make up the shortfall.
All this "would probably take the net cost of the EU to a higher level," Thurston said, adding that this could present a challenge for many countries that are already struggling with high budget deficits.
Who will decide?
Thurston said Germany could be seen as a "referee" between France and the UK in the highly polarised CAP reform debate. He recalled that the reason for "the current period of no reform since enlargement" was the deal done by Jacques Chirac and Gerhard Schröder to preserve the CAP budget until 2013.
That deal also included provisions preventing most of the money from going to the new member states after the 'big bang' enlargement to ten new countries, most of which are situated in much poorer parts of Eastern Europe.
But he believes it is more important to ask "who will be making the decisions on the CAP reform," because that will affect the final content of the policy.
"Depending on whether the decision-maker is the Agriculture Council, farm ministers or some higher level of government, such as finance ministers or heads of government, the outcome will be different," he stressed.
In any case, Thurston believes that France is now ready to accept "trading agriculture for some other aspects of European policymaking". French President Nicolas Sarkozy is not quite as committed to defending the CAP at all costs as his predecessor Jacques Chirac was, and could therefore be "more willing to countenance a trade-off on a bigger scale," he said.
European Parliament 'not that committed'
Thurston suggests that the European Parliament, a new major player on the CAP since the Lisbon Treaty gave it co-decision powers on the matter, does not seem very committed to agriculture either, apart from the agriculture committee.
While the committee wants to preserve the overall amount going to agriculture, albeit within a new co-financing mechanism, "the rest of the Parliament wants to free up €10-15 billion for something else". A co-financing deal could make that possible, he said.
Eastern member states after easy EU money
However, this smooth scenario might be disrupted by the new Eastern EU member states.
Countries like Poland and perhaps Romania and Bulgaria are eager to get their hands on "easy" EU cash for their farmers once their pre EU accession-related transition period is over.
CAP policies related to the "second pillar", which are related to environment and rural development policies, are seen as more complicated to implement because they require civil servants to draw up management contracts and conduct detailed monitoring and reporting, he said.
Therefore, Eastern countries which do not have very developed civil services to carry out more complicated programming are very keen on the first pillar, he added.
Even though everything about these countries suggests that the second pillar is what they need to boost their economic development, protect biodiversity and improve infrastructure, they seem to prefer the first pillar, Thurston said.