The supermarket's ivnestment in the coffee shop business has been much debated in the press in recent days because the chain retains the appearance of an independent company rather than one that is 49 per cent owned by the retail giant.
Clarke said in a blog that Tesco would back businesses "in which we see an opportunity for their brands to grow with ours", adding:
"Dobbies, another Tesco business, does this brilliantly with coffee shops which customers travel to just for the scones."
Clarke added: "We like backing great brands, helping them to grow and to realise their potential. We've done it with suppliers for years. Great ideas can find it hard to get backing these days, so we're pleased to be in a position to help entrepreneurs achieve their vision.
"We invested in Harris + Hoole after meeting entrepreneur Nick Tolley and his siblings Andrew and Laura, who are passionate about great coffee. They were looking for a company which could back their vision to bring quality coffee to a wider audience and we were impressed with their energy and enthusiasm.
"We thought customers would love the coffee and the warm, friendly atmosphere of their shops, so we decided to invest.
"Some people have asked why it's not branded Tesco. The H+H brand is part of its value – its distinctiveness and appeal. It's the Tolleys' business, their brand. Our investment helps them to take it further."
Clarke said H+H outlets would appear in Tesco stores "when the Tolleys are ready".
He said the Euphorium bakery was another example of Tesco's interest in backing businesses. Euphorium, founded in 1999 in Islington, north London, has an outlet in a Tesco store in Kensington.