Gordon Brown will have to manoeuvre around several traps if he is to minimise the political risks from the Irish rejection of the Lisbon treaty. He has two main aims: first, ensuring that Europe does not become a divisive and vote-losing issue at home, especially just before the next general election; secondly, retaining influence within the EU over what happens now and over what he considers the much more pressing issues of trade, rising energy prices, climate change and immigration.

The initial test comes this week with the third reading in the Lords tomorrow of the Lisbon treaty Bill, the final stage before it becomes law. Mr Brown has insisted that this will go ahead. David Miliband has said that it is “important that the British position is not in suspended animation, in limbo”. Ministers fear that, if the third reading is put off, Mr Brown will be in a weaker negotiating position at the EU summit this week.

The Tories want to suspend the ratification process. There are two options. The first, voting against the third reading, supporting a motion that “this Bill do not pass”, is the nuclear option because it would kill the legislation entirely. This would create a big political row because the Lords almost never votes down Bills in this way. Such a tactic is anyway unlikely to succeed.

The favoured option of the Conservative leadership is to put forward an amendment, in the name of Lord Howell of Guildford, the party's foreign affairs spokesman, which would delay the third reading. This would be presented, somewhat disingenuously given Tory opposition to the treaty, but seductively, as being in the spirit of the “period for reflection” mood being discussed by EU ministers. Such a motion would not kill the Bill because a third reading, say in October or November, would merely take a few hours, although such a delay would severely embarass Mr Brown this week. This amendment is intended to attract some Liberal Democrat and crossbench support, and could do so. Nonetheless, the odds are still that the Bill will get its third reading tomorrow, but the margin could be narrow.

Even if Mr Brown is able to tell fellow EU leaders on Thursday that the British have done their bit, he will still have to defuse calls from some EU leaders either to urge Ireland to hold a second referendum to reverse last Thursday's result or to bypass the Irish and to implement the treaty in the other 26 countries, which should all have ratified by later this year. Mr Miliband emphasised in the Commons last night that there would be no pressure on the Irish Government, which should be given time to make up its own mind.

The real British nightmare is the familiar and related one of a two-speed Europe in which an inner core led by France and Germany presses ahead with closer co-ordination in, say, defence and foreign policy. Moreover, given shifts in US attitudes, this development could possibly have the backing of the new American President taking office next January. This could present Mr Brown with awkward strategic choices and political controversies at home. An Irish “yes” vote would have been simpler for him. The European dog is seldom quiet for long.

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