Multiple working

Multiple Working is the term used in the UK where more than one operational diesel or electric locomotives are coupled together under the control of one driver. The term can also apply when diesel or electric multiple unit trains are coupled together and also under the control of one driver. 'In tandem' is the term usually used in the UK when more than one diesel or electric locomotive are hauling a single train and under the control of a driver on each locomotive.
If the front locomotive of a pair in multiple has failed the driver can still control the rear locomotive for as long as air and electricity supplies are available on the failed locomotive.