Cameron prepares 'nuclear option' on EU referendum The bill, introduced by James Wharton, a backbench Conservative MP, has passed the Commons and will this year go to the House of Lords for debate. In report on the bill, the Lords Constitution Committee said that parliamentary rules and timetables could cause the legislation to fail. It also warned that even if the bill becomes law, any referendum could be subject to court challenges. If the Lords make amendments to the Bill, those changes would have to be considered again by the Commons. There is only limited Commons time available for such consideration, with the last possible day for MPs to look at the Lords" changes falling next month. House of Lords rules "may make it unlikely that the bill would finish the Lords in time for any amendments passed by the Lords to be considered by the Commons on Friday 28 February 2014," the committee warned. Failure to get Mr Wharton's bill onto the statute book this year could expose the Conservative Party to attack from the UK Independence Party at the European Parliament elections in June. The House of Lords includes a significant number of pro-European politicians, who may attempt to change the legislation, and Conservative backers admit that the upper house could well kill of Mr Wharton's bill. Mr Wharton warned that the upper house would be defying public opinion if it thwarted his bill. He told the Telegraph: "It is ultimately up to members of the House of Lords whether this bill will be successful. But it would be very difficult to justify if the unelected House of Lords blocked a bill that has already passed every stage in the elected House of Commons and the purpose of which is to let the people decide on our membership of the EU. The prospect of resistance in the Lords has led Conservatives in the Commons to consider means of getting more time to debate Lords amendments Mr Wharton's bill. The Prime Minister told MPs last month he is ready to use the Parliament Act to overpower the House of Lords and get an EU referendum bill onto the statute book before 2015 The Act, which has been used only seven times in the past century, is sometimes described as the "nuclear" option of parliamentary process to break stalemates between the Commons and the Lords. It asserts the superiority of the House of Commons by allowing bills that cannot clear the Lords to become law, but is intended to be used only in exceptional circumstances. However, the Act could not be used on Mr Wharton's bill because it has already been introduced to Parliament. It could only be used on a new version of the bill introduced by another MP later this year.