When he was working as a cleaner to make ends meet, aspiring artist Alastair Barford wondered whether he would ever make a living as a painter. His future is looking rather brighter now, after he landed his first-ever commission: a portrait of the Queen.

Barford, 28, was hired by the Illustrated London News (ILN) to paint the Queen to mark the occasion of her becoming Britan’s longest-reigning monarch, a landmark she will reach on Wednesday.

As if that was not daunting enough for a first paid job, he had only 10 minutes to observe the Queen at close quarters during this year’s Garter ceremony, compared with the 40 hours he normally spends with a subject.

The result, however, is a far better likeness than many more famous artists have achieved with extensive sittings. Barford, from Bridport in Dorset, said: “The whole thing was quite a shock really. I had an email one Monday asking me if I would paint the Queen, and the next week I was at the Garter ceremony at Windsor Castle. “I was there for two hours, watching her from a distance, but I could only see her for about 10 minutes of that time. I made some sketches, got what I could, and had someone taking photographs, but it wasn’t a fantastic way of doing it.”

ILN, which has commissioned portraits of every monarch since Queen Victoria, wanted a new portrait for a one-off souvenir magazine and a limited-edition book set called The Record Reign. Its chief executive, Lisa Barnard, approached the Queen Elizabeth Scholarship Trust (QEST), the charitable arm of the Royal Warrant Holders’ Association, and asked if they could recommend a beneficiary of one of their scholarships to paint the portrait. Barford was at the time studying in Florence under Charles H Cecil using grants from QEST and the Leverhulme charity, and had completed just 20 portraits in his life, all of them as part of his studies. He said: “I studied fine art at Falmouth University, but after that I had to work part-time as a cleaner to make ends meet, while I was trying to develop as an artist and making a little bit of money here and there.

“Then I got the chance to come to Florence for three years, and I was just finishing my course when I was commissioned to paint the Queen. “It was an incredible opportunity, the best start you could imagine, but it was daunting, because painting her comes with a lot of expectations, as she means so much to so many people; yet I didn’t have a chance to get to know her, which I usually do with my subjects. “I found it difficult to get her expression right, and spent a lot of time painting her mouth, trying to capture her settled smile and her dignity.

“I’m satisfied with the result, but it’s hard to be pleased with any portrait, because you are always comparing it with what you hoped it would be.” Buckingham Palace, which usually allows up to two official portrait sittings with the Queen each year, agreed to allow Barford to attend the Garter ceremony in June, as ILN wanted to portray the Queen taking part in a public occasion, rather than sitting for a formal portrait.