THE SNP has banned its MPs from criticising the party, in a move that will help the leadership control political newcomers elected in May.

In a behind-closed-doors session, delegates voted to toughen up the rules for Westminster MPs.

The new standings orders state that any MP must "accept that no member shall within or outwith the parliament publicly criticise a group decision, policy or another member of the group".

The SNP declined to comment on the move but confirmed it was passed "overwhelmingly" by delegates.

It was criticised by the deputy leader of Scottish Labour, Kezia Dugdale, who said: "This is Stalinist discipline.

"But after the week she's had, it's understandable why Nicola Sturgeon should want to gag Alex Salmond."

A projection based on polling by the long-running British Election Study yesterday suggested the SNP was on course to win 47 of Scotland's 59 seats.

The result would return a number of inexperienced and untested candidates to Westminster.

In a separate move, delegates backed a series of measures designed to increase the number of women standing for the SNP in next year's Holyrood election.

Under the new rules, the party's governing national executive committee will be able to require local branches to draw up all-women shortlists in seats where a sitting MSP is retiring.

The governing body will also be able to add female candidates to shortlists, if the local party fails to include a woman, and alter regional list rankings.

SNP National Women's Officer Tasmina Ahmed-Sheikh said: "Today's move will enable our party to take reasonable and sensible action to ensure gender equality amongst our candidates and to guarantee that there are no longer any barriers to women playing a full role in the political process."

Meanwhile, a controversial European Union-US trade deal would be Thatcherism's "ultimate triumph" if left unaltered, according to an SNP candidate.

Chris Stephens, who is standing in Glasgow South West, told the party's conference the Transatlantic Trade and Investment Partnership (TTIP), which aims to remove barriers between the EU and the US, was a "dangerous attack on democracy".

Supporters say the trade deal would make it easier to buy and sell goods and services and open up markets, but critics fear it poses a threat to public services, particularly the health service.

The Scottish Government does not have a formal role in the ongoing negotiation.