Our employer is trying to take away our day off?

Our employers are currently trying to rewrite our rota to suit "the needs of the business". I totally understand that this but at the moment we start at 8.30am. They want us to start at 8am instead.. and also at the moment we work one in five weekends and in return we get the time in leiu by hours the week before and a day off the following friday.. this means we work 11days but get 3days off in a row the following weekend. The 11 days are hard but the friday off is a good incentive for this, However now they have decided to reduce the hours we work over 5 week period instead and remove the friday day off therefore meaning we will be working 12 consecutive days with the following weekend off. Is this legal. I have read the working directive but this doesnt seem to make much sense.