Europe remains a divisive issue in British politics. Over the next year we face a series of decisions, each of which could present problems for both Labour and the Tories.

That was underlined by the appearance yesterday at Downing Street of José Manuel Barroso, President of the European Commission. Gordon Brown praised his record since 2004 and backed him for a further five-year term, starting this autumn.

The European Parliament has the final say. But, before its vote, come Euro-elections in June. The Tories should do well, and last week said that, afterwards, they would quit the European People’s Party/European Democrats and form a new group. Mr Barroso, whose Portuguese party is in the EPP/ED, regretted the decision.

While obviously popular with the mainly sceptic Tory party, leaving the EPP/ED is not straightforward. It involves allying with nationalist Polish and Czech parties that hardly fit David Cameron’s more socially liberal image. This autumn also marks a second Irish referendum on the Lisbon treaty, which conventional wisdom (wrong last time) expects to favour approval.

One result would be that the December EU council will have to choose a president of the European Council, as distinct from the Commission. And Tony Blair, while still controversial, is back in the frame.

If the Lisbon treaty comes into force before the election, what will the Tories do? William Hague has talked of not letting it rest. What does that mean? Withdrawing from the treaty? Renegotiating Britain’s membership, as in 1974-75 (a token exercise)? This risks a clash with the rest of the EU.

Then, there is the euro. Some pro-Europeans see merit in joining to anchor market confidence in Britain during a slow recovery. Only Nick Clegg has raised the issue. It is anathema to the Tories, while Mr Brown also dismisses talk of the euro. But the option will return.

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