Local authorities often use their own employees to run polling stations during election days and to count votes once the polls have closed. This is because they can be sure that the staff will be available for training and are guaranteed time off from their real jobs, and because it’s easier to pay them as they’re already on the payroll.
Consequently, I have worked as a polling clerk (at the polling station) once and as a vote counter numerous times. Take it from me, the idea that you need to vote in pen to prevent people tampering with pencil votes isn’t just offensive, it’s laughable. Staff take the integrity of the process very seriously and would not condone or collude with vote tampering. Take a pen if you want, but there’s really no need.