Saw an article on the web advising to take your own pen to vote rather than using the pencil.
Checked if that was OK and it seems it is
"Do I have to mark my cross with a pencil on a string?
No, if you prefer you can use a pen, even if it's your own. While a cross is usually called for, you could theoretically mark the box with a tick instead. The important thing is that your voting intention is clear."
www.bbc.co.uk/news/magazine-32451429