The future role of the European Court of Justice (ECJ) under the proposed European constitution is ambiguous and needs to be clarified by the government, a House of Lords committee said this week.

The report by the Lords' European Union committee recommended that the government set out its view on whether the ECJ or national courts should be the ultimate arbiter of the dividing line between the UK and EU law.

Although Parliament has recognised that the ECJ has jurisdiction in relation to European treaties, there remains scope for claims that parliamentary sovereignty and EU law could be in conflict.

The report said: 'The government should set out its view on the [competence] question clearly to Parliament and to citizens in the UK.

This could go a long way in assuring the public that the union is not some Frankenstein creation over which there may be little or no control.'

The report also said that the draft remains ambiguous on the issue of whether the court has primacy over national courts only in relation to EU law with direct effect, or whether it would extend such primacy.

Oxford University's Professor Paul Craig, one of the committee's witnesses, said that if the issue of primacy was left ambiguous, 'you are going to get a nuclear problem which is going to have to be resolved either prior to or post-ratification'.

Lord Clinton-Davis, the former European Commissioner and consultant with City firm SJ Berwin - who sat on the committee - said: 'I hope the arguments we have put forward will be listened to by government.

We have listened to many people and the committee itself has unparalleled expertise.'

Jeremy Fleming