Just done a bit of checking and look what I found. Click the links.
As you'll see, in most cases GNER have provided a variation of excuses to justify increased parking fees at each station. These range from, bring fees into line with other local parking charges, Increase spaces, cover costs of CCTV, to cover the costs of their franchise which incidentally, many feel they overpaid (or rather their customers will)
http://news.bbc.co.uk/1/hi/england/south_yorkshire/5089240.stm
http://www.granthamtoday.co.uk/ViewArticle2.aspx?SectionID=833&ArticleID=1582803
http://news.bbc.co.uk/1/hi/england/5138768.stm?ls
http://www.peterboroughtoday.co.uk/ViewArticle2.aspx?SectionID=845&ArticleID=1576127
The words Grabbing, Bastards and Money spring to mind though not necessarily in that order.












