Thankyou for all the advice chaps! As i'm travelling at the moment, the blocking of anything is at best difficult. Apart from the steps taken in the OP, I also deleted Safari and all it's associated files and then re-installed it, sadly to the same state as before. Mr Bushfiva's link seems to have provided the solution (fingers crossed).
The culprits were 'Adware.Awesome Screenshot' and 'Adware.Crossrider' hidden away in the launch items where 'MyShopMate' and 'Software-Updater.agent were causing browsing havoc. The effects have been sporadically persistent , even when logging into pprune, the moment the cursor touched the box up popped another window of supposed linked content. Thankfully DIDN'T do anything whilst checking e-mails. This is my 1st experience with malware, and in general i'm pretty careful. My laptop is an older Apple MBP running Mountain Lion, serves me very well in most cases, but now and again certain websites can't function as they are set up to liase with the more up to date OS's etc, and i do get messages saying that i need to upgrade to the latest version of XYZ to use the facilities. How do 'we' tell the good from the bad in such cases ?
Thanks again for help.