BENDING leadership rules to favour Boris Johnson would risk "swamping" the Conservative Party with entryists, causing long-term damage, Lord Hague has warned.

The former party leader said the grassroots should not be given too much say in a leadership vote, which could risk a Jeremy Corbyn-style split.

At present, only two leadership candidates go to a final vote, a rule set under Lord Hague's leadership. However, some activists want any MP with the support of 20 colleagues to go through.

The Tory peer compared the idea to Labour's rule change of 2015, when opening up its membership led to a surge in hard-left supporters and the election of Mr Corbyn, which, he claimed, had left democracy "fundamentally weaker".

Lord Hague, a former Foreign Secretary, said the proposed change would help Mr Johnson, "who is currently thought to be more popular with the party members than with parliamentarians".

But he warned it would put too much power in the hands of Tory activists, who, he argued, were “often the first to point out that they are not remotely representative of society at large or even of their voters".

Lord Hague highlighted a call by Leave.EU, a hard Brexit campaign group said to have almost 90,000 supporters, for them to "flood" the Conservative Party to ensure a "true Brexiteer" like Mr Johnson became prime minister.

His reform gave party members the deciding vote in a leadership contest for the first time. The former leader said he had hoped the rules would lead to the revival of the Conservative grassroots but had been proved "spectacularly wrong" after membership of the party halved to its current level of just 124,000.

"A small membership is then at risk at any time of being swamped by a sudden influx of new recruits; the very thing that happened in Labour in 2015," the Tory peer wrote in the Daily Telegraph.

Earlier in the week, Conservative backbencher Anna Soubry, the pro-EU former Business Minister, pointed out how the Brexiteer faction were “absolutely dedicated to their cause”.

She added: “You don’t need an awful lot of people to make a huge amount of difference, so it’s really worrying.”

Her Tory colleague George Freeman admitted he too was very worried about how the party’s future could be re-directed.

“We must resist pressure from Nigel Farage, an unaccountable unelected rabble-rouser pushing a hard Right nationalist agenda, to distort the Conservative membership.

“We should...fight instead for mainstream voters abandoned by Corbyn,” he added.