Are you legally obliged to work your notice?
As long as you haven't breached the contract, you don't have to pay someone for their notice if they refuse to work it. Do you have to work your notice period? Yes, employees will normally be contractually obligated to work their notice period. If staff sign the contract, they must adhere to it.
Can you just walk out of a job?
Your employer can't restrain you from leaving the building, so there's no chance of you being physically stopped if you were to pack up your personal belongings, walk out the door and not return. However, if you leave without serving the correct notice period, you're likely to be breaching your contract.