How many signatures are required to start the formal decision making stage of a direct democracy mechanism?

UK Public General Acts, Recall of MPs Act 2015, accessed 26 January 2021

14. Determination of whether recall petition successful

(3) For the purposes of this Act, a recall petition is successful if the number of persons who validly sign the petition is at least 10% of the number of eligible registered electors.

“The number of eligible registered electors” is the number of persons registered in the register of parliamentary electors for the constituency on the last day of the signing period excluding those who, according to their entry in the register, are aged under 18 on that day.

At least 10% of the eligible registered electors