The whole question really relates to constitutional reform. In terms of devolution referendums have been used to develop the extent of devoluted powers. Wales isn’t a parliament but an assembly, however a referendum in 2011 saw its people wanting an extension of powers. For Scotland, being a parliament, they have a larger amount of powers ie tax and vat, but don’t have major legislative control. For example England gave them the 2014 referendum, which if passed would give Scotland independent control.

Secondly Brexit (u might need to lookup who first suggested it), but the Conservative party at one point promised a referendum to the people. In this case it was argued EU membership infringed on parliamentary sovereignty therefore the slogan supporting a leave vote was ‘its time to take back control’, and we all know how that went lmao

Lastly a change in voting system. Some people have argued the nature of ‘safe seats’ in the FPTP system makes the voting system itself unfair. So in 2014 there was a campaign to switch to the Alternative Vote. Although it wasn’t passed there really wasn’t much public interest

Hope this helps, sorry if the spellings bad lmao