I'm getting the same message on my 18866 calls this morning and, checking the online 'Last Calls' list, they are, indeed, £0.0099 each, regardless of length (although my longest call so far has only been 7½ minutes).
The bad news is that the 7½ minute call dropped out and I had to redial - another 1p connection!
Because there are other reports of call dropouts on
http://forum.moneysavingexpert.com/cgi-bin/yabb/YaBB.cgi?board=Telephone;action=... I reported the dropout as a fault to 18866 via their website.
Update. Used 18866 for a 41½ minute UK ‘01’ call this evening without dropout - so it probably was just a ‘glitch’ this morning.