Rig an election?

[Combwork]

How difficult would it be to rig an election, not so's to make one party win but to take votes away from another party.

The way U.K. elections work is everyone on the electoral role who wants to vote goes to the poling station, gets a voting slip with names and a box by each name. They have to mark an X against one name only (in pencil would you believe). Any marks outside the box or marking more than one gets the vote nullified.

Any thoughts gentlemen?