We have been here before - they cling those suckers.
A professional scraper will do the trick... £8.94 from Amazon post free...
http://www.amazon.co.uk/Stanley-Duty-Long-Handle-Scraper/dp/B0001IW630/ref=sr_1_10?ie=UTF8&qid=1370617143&sr=8-10&keywords=professional+scraper
Peccavi
June 2013