The Conservatives should not change the rules to make it easier to elect Boris Johnson because it could damage the party in the long term, William Hague has warned.

The former party leader says that giving grassroots Tories a greater say in the election of their next leader could lead to entryism and see the party “swamped by new recruits”.

He compares the proposal to Labour’s rule changes in 2015, where opening up the membership of the party ultimately led to the election of Jeremy Corbyn, leaving democracy “fundamentally weaker”.

It comes as grassroots Tory activists are trying to pressure the party’s ruling board to change the rules so that any MP with the support of 20 colleagues can go forward to the final ballot of party members. At present only two MPs go through to the final vote.

Lord Hague, the former foreign secretary, says: “Such a change would be seen as helping ... Boris Johnson, who is currently thought to be more popular with the party members than with parliamentarians."