I'm reading the book Slate Mining in the Lake District by Alastair Cameron and it called it Petts. It went bust in 2012 and was bough by Burlington
http://www.thewestmorlandgazette.co.uk/news/9707126.Burlington_takes_on_failed_firm_s_quarry/
On their website they call it Petts, http://www.burlingtonstone.co.uk/company/heritage/
From the horses mouth? however if you feel it's wrong, please do as you wish, I'm not attached to it ;-)