Theresa May’s conference speech is likely to be followed by an opening offer of £20-30bn for the Brexit bill

Theresa May is set to approve a politically explosive Brexit bill of up to £50bn after the Conservative Party conference in October in an effort to kickstart trade talks with the European Union.

Under plans being drawn up in Whitehall, Britain would pay between £7bn and £17bn a year to Brussels for three years after Brexit before ending sizeable direct payments into EU coffers in time for the 2022 general election.

But May and her Brexit secretary, David Davis, risk accusations that they are keeping their intentions secret to protect the prime minister from attacks by Eurosceptics at a conference where she will fight to re-establish credibility.

Brussels is demanding a Brexit bill of €100bn (£92bn), but senior Tories say Britain will open with a