It can be extremely jarring if your electricity supply is disconnected. There are a number of reasons for this, from routine works to network faults or simply because your supplier has cut you off for non-payment of bills.
If your DNO disconnects your energy to carry out routine maintenance, they are required to provide at least 2 days notice. If you do not receive this, or you are disconnected for more than 24 hours due to a network problem, you may be entitled to compensation. Your DNO will reconnect your supply as soon as it is able.
If, on the other hand, you have been disconnected by your supplier, only they can reconnect you. This may incur charges which will usually be folded into a repayment plan that you arrange with your supplier as a condition of reconnection.