A Turing machine is a theoretical mathematical device invented by Alan Turing (1912-54), a British mathematician, in the 1930s. The theory was influential in the development of computer science and the modern-day computer.
The Scottish physician and researcher John MacLeod (1876-1935) was the co-discoverer of insulin, used to treat diabetes.
The structure of the DNA molecule was discovered in 1953 through work at British universities in London and Cambridge. This discovery contributed to many scientific advances, particularly in medicine and fighting crime. Francis Crick (1916-2004), one of those awarded the Nobel Prize for this discovery, was British.