Russia's influence reaches deep into the British establishment and successive UK governments have turned a blind eye to it, lawmakers were warned, according to multiple sources familiar with testimony given to a parliamentary inquiry.

Sources say company has run seemingly independent pro-Brexit campaigns since 2017.

It is the government’s responsibility to defend against election interference and tackle the broken market that lets it flourish. Failure to do so is a dereliction of its democratic duty.

Investigation follows revelations of Lynton Crosby firm running ad campaign calling voters to lobby MPs.

A series of hugely influential Facebook advertising campaigns that appear to be separate grassroots movements for a no-deal Brexit are secretly overseen by employees of Sir Lynton Crosby’s lobbying company and a former adviser to Boris Johnson, documents seen by the Guardian reveal.