Coventry BS historical interest rates

Anybody know whether there's an easily accessible database on Coventry's mortgage interest rate history? Looking at going onto their 'Flexx for Term mortgage' , but as it isn't a tracker, I'd like to see how the rate has behaved over time - to see what the effective cost of the offset facility is and the behaviour of the rate vs trackers. Competitive pressures should keep it in line but what should be and what is often don't coincide.
Thanks!