Conservative backbencher Douglas Carswell is joining forces with Green MP Caroline Lucas in a bid to give voters the option of proportional representation in May's electoral reform referendum.

At the moment, there will only be one option on the ballot paper - the Alternative Vote system.

But Mr Carswell says this will make MPs less representative than they are now.

He said he planned to move a series of amendments in the Commons next week, with Caroline Lucas, to the Electoral Reform Bill currently making its way through Parliament, to give voters the "fullest range of options possible" in the referendum.

Speaking at a fringe meeting at the Conservative Party conference in Birmingham, Mr Carswell said: "Those of us who believe in far reaching political reform should vote no to AV."

He argued that AV, under which voters rank candidates in order of preference, would "insulate many politicians from their voters" because candidates would be able to "ignore" the views of those who did not support them, safe in the knowledge that they would get second or third preference votes.

Ireland

He said it was "a reform that was picked by politicians trying to cobble together a coalition in order to gain power" and it would "guarantee that we move to an even more bland and generic way of doing politics".

The Lib Dems demanded a referendum on AV as part of their power sharing deal with the Conservatives, even though most Tories favour the current first-past-post system and the party leadership will campaign to keep it.

Mr Carswell is unusual among his backbench Conservative colleagues in campaigning for a more proportional voting system, arguing in favour of the single, transferable vote system like the one used in Ireland.

Constituencies would have three MPs and each voter would get one vote, which can transfer from their first preference to their second preference and so on, as necessary.

Ms Lucas also backs more proportional voting, either with the single transferable vote system (STV) or the additional member system (AMS), under which MPs from a party list are added to their total to reflect the share of their vote.

The amendment worked out between Ms Lucas and Mr Carswell, says voters should be asked if they want to keep the status quo, and if not which of four voting systems would they prefer - AV, STV, AMS or AV Plus, where top-up seats are allocated in line with a party's share of the vote.

'Knaves and charlatans'

Mr Carswell said he hoped to attract support from "centre left" MPs and Lib Dems, who want electoral reform but are against AV.

Conservative MEP Daniel Hannan also spoke out against AV at the meeting, saying those who were campaigning for it risked appearing "knaves and charlatans" and he accused the Electoral Reform Society of "risking making utter fools of themselves" after spending so many years campaigning for proportional representation.

He said there was a case for PR but the most important changes were open primaries to select election candidates and more referendums.

Peter Facey, of Unlock Democracy, one of the leading campaigners for AV, was one of three people on the seven strong panel to argue in favour of the system, saying voters deserved more choice.

Author Peter Stafford also made an impassioned argument for AV, saying British democracy was "broken, bankrupt, it is not fair and it is time for it to change".

David Campbell-Bannerman, deputy leader of the UK Independence Party, who was in the audience at the Freedom Zone fringe meeting, said he had persuaded Conservative MP Philip Hollobone to table an amendment calling for voters to be asked if they want AV Plus, which he believes is fairer.