Yup mainly tried it with postal votes which are signature verified as coming from the registered voter (as they are in this country) before the actual ballot papers also enclosed are added to the secret ballot. It would be incredibly hard to commit postal vote election fraud on any scale to defraud an election.totally unfounded and thrown out by every court he tried his luck with.
Meanwhile the Tories managed to defraud the public by putting up a PCC candidate who ineligible to hold the office despite him declaring to the selection committee his offence. https://www.bbc.co.uk/news/uk-england-wiltshire-57048309 so not only costing the British public the cost of an election and the rerun. But any costs incurred by those running against him and hours of volunteer work in an election that meant the winner couldn't win.
Have to worry about something that might happen though not stuff that actually does or proven that will through trials.