Any tax experts out there?

My company has a deferred compensation policy and I've been given deferred shares vesting in 2011 and 2012

The questions is: If i'm given the shares at say £1 and the share price is £1.20 in 2011/2 do I pay tax on the £1 price or the £1.20 price? Also which tax price applies if the share price drops to 80p?

Don't think I'll reach the capital gains tax thresholds unless the price rockets though

thanks