Is this Mary Tudor, England’s Catholic queen who has gone down in schoolroom history as Bloody Mary?

If it is, as some scholars believe, the painting could make a virtuous circle to delight the heart of a Home Counties Jesuit parish priest. “It could be a small miracle,” says Canon Timothy Russ. And the secrets it contains could also bear new witness to the torrid religious politics of the mid-16th century.

Canon Russ is prepared to sell the painting he inherited in order to rescue Sawston Hall, near Cambridge, the 16th-century home of the recusant Huddleston family, and turn it into a Catholic heritage centre and refuge.

After the death of her brother Edward VI in July 1553, Mary Tudor was pursued by Robert Dudley, son of the chief minister, the Duke of Northumberland. She took refuge at Sawston and was smuggled away as her pursuers closed in. Dudley burnt the house down and Mary promised to rebuild it for the Huddlestons, and she was true to her word.

After her death in 1558 Sawston became a safe house for persecuted Catholic priests. The family remained there until 1980 when Sawston Hall was left by Canon Russ’s great-uncle to a cousin and it was eventually sold to a developer whose plans foundered. It is now for sale at £5 million.

But the contents, including the portrait, had been left to Canon Russ. The painting, oil on panel, is an unsigned full-length portrait of a lady, in black and wearing no jewellery. Tests on the panel in the 1970s date it to the 1550s, and it has been attributed to William Scrots, the court painter who succeeded Holbein. It was first exhibited at the Royal Academy in 1956 and firmly ascribed as Mary I, but since then the identity has been doubted. Exhibited at the Tate in 1969-70 in an exhibition curated by Sir Roy Strong, the title was downgraded to Called Mary I, and by the Tate’s Destinies exhibition 1995 it had become A Lady in Black.

This year it was seen by Dr Tarnya Cooper, 16th-century curator at the National Portrait Gallery. “We concluded that while it is undoubtedly a very interesting and important painting, it cannot represent Mary I mainly because of facial dissimilarity with other authentic portraits of her. It is more likely to be a member of the nobility, possibly from within Princess Mary’s circle,” she said.

Sir Roy Strong, former director of the NPG and an authority on Tudor portraiture, is a patron of the charity set up to save Sawston. He said he has never been convinced that the portrait is of Mary, “and I have seen nothing to change my mind. The mid-16th century was a very dark time and it is extremely difficult to be certain.” But Professor Jack Scarisbrick, the Tudor and Catholic scholar, says it is too grand a portrait to be of anyone but royalty. “There was nobody outside the royal family important enough for such a lavish full-length painting — and if it is isn’t Mary, who is it? Nobody else fits the bill,” he said.

So convinced is Linda Porter, the author of a recent biography of Mary Tudor, of the sitter that she used the image on the cover of her book. “I’m certain it’s Mary,” she said. “It was quite fashionable in the last decades of the 20th century to question the identity of sitters in several well-known Tudor portraits, but some of this scepticism has now come full circle — the portrait of Katherine Howard that was questioned at this period is now thought to, indeed, be her. My own view is that family traditions are very often reliable. Plus which, to me at least, it looks like her.”

There are, she says, distinct similarities in other verified portraits of the queen, such as the one by Antonio Moro of the 1550s, now in the Isabella Stewart Gardner Museum, Boston.

But Canon Russ has identified more in the painting than the portrait. It is a puzzle picture, with secret messages in the background. The ruins, painted in blood red, behind the sitter could denote the Reformation destruction of Catholic churches and proscripton of priests; a head to her right showing a triple crown tumbling off it could be the rejection of the Pope; to her left, there appear to be several profiles, at least one of which could be Henry VIII; and at the foot of the column to her left appears what could be a baby in swaddling.

This, he and Professor Scarisbrick, who is also a patron of the Sawston appeal (with Cardinal Cormack Murphy O’Connor and the Archbishop of Canterbury), believe to be the crucial clue, representing the new-born Edward who superseded her in line to the throne.

The sitter could be in mourning for Edward’s mother, Jane Seymour, who died giving birth, explaining the lack of jewellery, of which Mary was fond. She dangles what seems to be a watch, the thief of time. However, this would date the painting to much earlier: Edward VI was born and his mother died in October 1537, when Mary had been seriously ill and only recently restored to her father’s favour.

Which, says Canon Russ, suggests another surprise: could it be by Holbein himself? He died in 1543 and his most famous puzzle painting is The Ambassadors of 1533, but the suggestion is rejected by Strong who says it is not in Holbein’s style.