An employer would find it very hard to make a 30 mile clause stick at a tribunal, especially in such hard employment times. the employer cannot have it all his/her own way , you are already on a 4 day week .what if this is reduced further , can you be dead sure it won't be-- of course not.Are you in a union , if so check the legitimacy of this clause , if not ring ACAS. I would begin looking actively for a new job, stall signing anything, and do not discuss with your fellow workers what you are up to. If forced to sign , cross out that clause and claim temporary insanity.(joking), ask for another contract and begin stalling again.You never know they may forget you haven't done it.good luck.