Theresa May treated Michael Heseltine like a “two-bit backbencher” and is sowing the seeds of her own downfall in the way she deals with her party, ex-Deputy Prime Minister Nick Clegg has warned.

The former Liberal Democrat leader said Tory peer Lord Heseltine’s sudden sacking as a government adviser, without so much as a phone call from Ms May, had exposed a callous streak that would come back to haunt the Prime Minister.

In an exclusive interview with The Independent, he said resentment is building among Tories over Ms May’s broader “disrespectful and authoritarian” approach, as she tries to force through her Brexit bill with only the slimmest of Commons majorities.

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His words come as the Government faces a second backbench rebellion in a matter of days, this time over Ms May’s refusal to allow Parliament a full say in deciding the country’s future once she has concluded Brexit negotiations. It also follows a friendly breakfast Mr Clegg shared with Tory ex-leader David Cameron.

Former Cabinet minister Lord Heseltine was Mr Cameron’s devolution tsar under the former leader’s Conservative administration and before that under the coalition, where he also worked alongside Mr Clegg.

But when the Tory peer dared to back an amendment to Ms May’s Brexit bill that would see Parliament, and not Downing Street, given the final say on the country’s future relations with the EU, he was immediately sacked.

The peer did not complain, but it did emerge that he had simply received a call summoning him to the whip's office halfway through a dinner with his wife and was told he no longer had his job. He later revealed the Prime Minister had not spoken to him since she took the keys to No 10.

Speaking to The Independent, Mr Clegg said: “You do not treat a genuinely venerable character like Michael Heseltine like some two-bit backbencher. She didn’t even talk to him.

“I happened to have worked closely with Michael Heseltine and I believe, that among the many plethora of things he did, he did a great, a great job, for the coalition. He’s one of those big beasts that you treat with respect.

“If you start kicking at people in such a disrespectful way, it always catches up with you. It’s always the same in life. Be careful what you do on the way up, because you’ll need some friends as you go down. I think Theresa May has forgotten that golden rule.”

The Prime Minister launched her tenure in office with a ruthlessly decisive round of ministerial sackings, which both cleared out allies of Mr Cameron and George Osborne and created a group of potential enemies on her back bench.

She has a reputation for consulting only a small inner circle of aides, and has brought a host of former Home Office allies to Downing Street with her.

Her attempt to trigger Brexit using the Queen’s royal powers, without giving MPs of any party a say, saw the Government taken to the Supreme Court where they were told by judges that Parliament has a right to vote on invoking Article 50.

Lib Dem MP Mr Cleg went on: “Theresa May is underestimating how much subterranean resentment she is building up against the way she is running things from within the Conservative Party.

“I’ve been in politics long enough now, I’ve done it myself, to know that first you go up, everyone thinks you’ve got gravity defying powers, but I tell you, for every rise there is always a fall, as there will be with Theresa May. Regimes end, special advisers come and go.

“She is treating her own side with a disrespectful and authoritarian demeanour that over time they will come to resent.”

Mr Clegg was seen having breakfast with his former coalition partner Mr Cameron at the Ivy Brasserie, in west London, shortly before last week's Budget and his interview with The Independent. After the statement the Tory ex-PM was seen apparently attacking the "stupidity" of a key measure announced.

The Lib Dem's intervention comes ahead of a critical vote in the House of Commons tonight on Ms May’s Article 50 bill, which could see Conservative MPs defy the Prime Minister in the same way Tory Lords have already done in the upper chamber.

If ministers do not make clearer their intention to give Parliament a proper vote on what happens after Article 50 negotiations end, Tory MPs have threatened to rebel and force the Prime Minister to accept an amendment that guarantees in statute their right to approve any deal, or any move to withdraw from the EU with no deal.

The threat of having the right to vote written in law, could force Brexit Secretary David Davis to make a statement in the Commons on Monday outlining that MPs and peers will get to have a final say.

One Tory MP told The Independent: “A loss for the Government on the amendment is a possibility. There are enough people who are very cross. There are people who voted with the Government last time who this time will say, if you’re going to be this intransigent then we can’t vote with you now.

“They shouldn’t simply rely on the fact that things will stay the same from the last vote. The same verbal assurance as last time is not enough.”

Another MP said: “The ball is in their court. We need an assurance that Parliament will have a say in the event of the ‘no deal’ scenario.”

The standoff follows another row over the Government’s plan announced in Philip Hammond’s Budget to increase National Insurance contributions paid by 1.6 million self-employed people, despite the Tories’ 2015 election manifesto clearly and repeatedly stating NICs would be frozen.

Conservative MPs shocked that the Chancellor had chosen to hit “our people” – entrepreneurs and small business owners – with a significant tax hike, took to the airwaves to raise their concerns.

Their anger was exacerbated by the Government’s attempts to deny the manifesto pledge had been breached, by saying detail of the policy had been published after the election.