Mr Day, who owns Edinburgh Woollen Mill, has once again appeared on the Rich List which records his wealth as £1.2bn.
It might have been a disappointing year for Rory McIlroy out on the course last year, but that did not seem to interfere much with his earning power, as the 29-year-old from Northern Ireland has still been named the wealthiest sports person under the age of 30 by the Sunday Times Rich list.
Sir Len Balvatnik was listed in third place at £15.26bn, after being knighted this year for services to philanthropy.
This year is the 30th anniversary of the Rich List, with the top 20 now worth a combined £218.6 billion - increasing their cumulative wealth by £33.
Of the 1,000 people on the list, 145 are billionaires.
Meanwhile, disgraced ex-BHS boss Sir Philip Green's wealth tumbled £787m to £2bn following sales failures at Topshop and Miss Selfridge, as well as a commitment to paying £363m to settle the BHS pension scheme.
The richest man in Cumbria Philip Day has seen his fortune grow by £50m in the past year - ranking him among the wealthiest people in the north west of England.
The Grosvenor Estate includes large holdings in London, including 300 acres in Mayfair and Belgravia, as well as properties in Oxford, Cheshire, Scotland and Spain. The wealth of Glenn Gordon and his family, who also topped the Scottish list previous year, grew by £606 million over the past 12 months to £2.572 billion.
Robert Watts, who compiled the list, said: "Britain is changing".
Take a look through the gallery above to see the Sunday Times Rich List for young sports stars in 2018.