Just an update to let everyone know the problem was fixed.
Eventually I gave up trying to install the pepper-flash package, and instead installed google-chrome which comes with the latest flash player. Low and behold, I then tried to install the pepper-flash player for chromium and it installed without any problems. The reason being, by installing google-chrome all the dependancies for pepper-flash were already installed by google-chrome and hence there were no dependancies require for pepper-flash the second time round.
One other thing worth noting, pepper-flash is only accessable by chromium and not other browsers like Iceweasel.