This time last year a call minute was priced at 5.4 pence. By my reckoning the year on year increase has actually been more like a 40% increase. See my note in February 2010. Of course that is not all. The call set up fee will increase to 12.5 pence (last year in Feb 9.3 pence - that is a 35% increase).
So from the 1st of April 2011, if you make a BT call and speak for 10 seconds it will cost you 20.1 pence. The price of a similar call via Skype: 5.8 pence (including VAT).