Builder’s tea is the nickname for a mug of (usually strong) English Breakfast tea (or in Ireland, Irish Breakfast Tea), usually served with milk and, often, one or more sugars. It is so-named because it has the reputation of being the favorite drink of construction workers and home improver when taking a break. Back in 1916, the ministry of Munitions' health committee wrote in a publication called 'Hours of Work', 'an opportunity for tea is regarded as beneficial both to health and output'.
This still holds true today and not just for builders. This style of tea is a mainstay of the office tea break, with many executives enjoying its refreshing qualities.