Britain's Prime Minister Theresa May looks on during a general election campaign visit to a tool factory in Kelso, Scotland June 5, 2017. [Photo/Agencies]

The poll was conducted on Friday and Saturday, before an attack in London by Islamist militants that killed seven people and injured 48.

In the previous Survation poll for ITV, published a week ago, the Conservatives had a lead of six points. But a separate Survation poll, published on Saturday for the Mail on Sunday newspaper, also gave the Conservatives a one-point lead.

Survation said its latest poll put support for May's Conservative Party at 41.5 percent compared with 40.4 percent for Labour, a result which if replicated in the election would put in jeopardy the Conservatives' majority in parliament.

Opinion polls by other leading polling firms have given wider leads for the Conservatives in recent days, ranging as high as 11 and 12 points.

Monday's Survation/ITV poll was based on interviews with 1,103 people.