Sir John Major has launched a scathing attack on “zealot” Tory Brexiteers, accusing ”extreme” Conservative MPs of acting as “a party within a party”.

In a move likely to fuel Tory warfare over Brexit, the former prime minister accused some members of the European Research Group (ERG) of Conservative MPs of having “little or nor affinity to moderate, pragmatic and tolerant Conservatism”.

He said the Conservatives and Labour were both being “mainpulated by fringe opinion” and claimed right-wingers in his own party were shaping government policy “simply by being intransigent”.

Sir John urged moderate Conservative MPs to stay in the party rather than join the new Independent Group, insisting Tory and Labour MPs need to force their parties towards the political centre.

In a speech at the University of Glasgow, he said: “Currently, both the Conservative and Labour parties are being manipulated by fringe opinion. The rationale for extremists joining mainstream parties is logical: from within them, they can influence policy; from without, they very rarely can.

“The Conservative Party membership appears to be ‘hollowing out’ traditional Conservatives, while former Ukip members strengthen the anti-European right of the party.”

In a blistering attack on Jacob Rees-Mogg‘s ERG, he continued: “In parliament, the European Research Group has become a party within a party, with its own whips, its own funding and its own priorities. Some of its more extreme members have little or no affinity to moderate, pragmatic and tolerant Conservatism.

“The ERG does not represent a majority view, but with a minority government – as now – can determine policy simply by being intransigent, which is precisely what it is doing.

“Some – who can fairly be called zealots – seem incapable of looking beyond the one issue of Europe. It’s not just that it dominates their thinking – it seems to obsess them.”

Sir John was speaking after seven MPs resigned from the Labour Party to form a new parliamentary grouping. The former prime minister said he admired their “courage and their conviction” but hoped they had not “cut themselves adrift forever” because Labour needed moderate MPs inside the party.

Top politicians' Brexit tweets haven't aged well Show all 18 1 /18 Top politicians' Brexit tweets haven't aged well Top politicians' Brexit tweets haven't aged well These billboards were plastered by campaign group Led By Donkeys @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well Undated handout photo issued by Led by Donkeys of their billboard featuring a blank tweet in Jeremy Corbyn's Islington North constituency in protest over what they claim is his lack of leadership on Brexit. PRESS ASSOCIATION Photo. Issue date: Tuesday February 12, 2019. For the past month, campaign group Led by Donkeys has been putting up posters all over the country featuring quotes mostly from hard-Brexit MPs which claimed the process of leaving the EU would be easy. The Labour leader is the group's latest target because of his failure to back a second referendum on Brexit. See PA story PROTEST Donkeys. Photo credit should read: Led by Donkeys /PA Wire NOTE TO EDITORS: This handout photo may only be used in for editorial reporting purposes for the contemporaneous illustration of events, things or the people in the image or facts mentioned in the caption. Reuse of the picture may require further permission from the copyright holder. PA Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter Top politicians' Brexit tweets haven't aged well @ByDonkeys / Twitter

He also urged potential defectors in his own party to stay put, saying they had a “duty” to ensure the Tories “retain a mainstream majority of their own”.

He said: “When I refer to ‘the centre’, I don’t mean some amorphous new party of ‘moderates’ and ‘centrists’. Even if such a party were elected, what would unfold when it fell out of favour? For all governments are mortal.

“With mainstream opinion sidelined, the country’s only choice would be between the extremes of left or right. That would be an awful outcome. Our electorate needs a choice between parties that are demonstrably rational, realistic and sane.