Always worth a try..
Download and run Malwarebytes, might fix it. Sounds like malware .Not all is found by Antivirus Software.
http://www.malwarebytes.org/mbam.php
Me too Neil, luckily we filled up in October when it was 40p, so should be ok for a few more months yet. Hopefully it'll come back down again!
Just filled mine 1000 ltrs at..............65p per litre. (it will last 8 weeks)