Smart Pensions. Cable and Wireless run such a scheme and I have found the following link to the company handbook that explains it.
http://www.freedom.cw.com/pdf/Smart_Booklet.pdf
Page 5 is the interesting one, especially part for people on the notional 50 grand a year salary. £20 a year for the massive savings the company are making does not seem a lot.
As for benefits on retirement, in the C&W scheme there is no change, it quite clearly states on page 8 that nothing will change as the final salary used to calculate the pension will be based on the "notional" final salary.
As long as it is negotiated that benefits are based on notional salary the only loser is the taxman. However Where we do lose out though is when we have pay rises of greater than RPI + 0.5%, in which case your actually salary becomes higher than the notional salary.