This is a letter from Brett Dolman, Curator of Collections at Hampton Court who states that these are his informal thoughts ;
Dear Mrs. Mostyn,
Thank you for your letter of the 27th.January, regarding the Sawston Hall portrait of a lady in black, now at Sotheby's; I am so sorry it has taken so long to reply. I was hoping to have found the time to see the lady herself by now - hence the delay - but my work at Hampton Court has prevented me from getting to Sotheby's before Easter. I hope to be able to arrange a visit very soon, but I thought that you deserved at least a short letter in the meantime.
I am afraid, however, that I have very little to add to what I've already said to Christopher Wickham and to Canon Russ on the telephone. I am not convinced that this is a portrait of Mary l, and I generally take the position that without a 'smoking gun', clear identifications are all but impossible. It is not fair to say to-day, I think, that experts are too quick to dismiss supposed identifications of portraits; it is more the case that in the 19th century, many portraits seem to have been assigned identities on no other evidence than passing physiognomic or costume resemblance to another (often equally uncertain) portrait. We remain susceptible to this urge, as we are frustrated that we lack portraits of key figures from important periods of history, whilst the potraits that do survive are in many cases unidentified. The temptation to fit the portraits with our preferred list of candidates is huge, but unless there is intrinsic evidence in the painting itself (a contemporary inscription, a specific jewel perhaps, or a traceable physical link to another portrait) or independent evidence (a document that describes the painting or the commission) then all such identifications remain suspect.
I was, nonetheless, extremely interested to read the proposed allegorical symbolism in detail, but I am afraid much of this remains elusive (I cannot see much more than an outline of a man in the column on the far left of the sitter) and there is a more general problem with artistic intent here which I think is worth making: I don't think it would have occured to an artist of this period to producea portrait with this amount of hidden iconographic detailing. It remains possible that he was instructed so to do, but without idependent proof of the sitter's identity, we cannot draw too many conclusions. Morover, iconographic or allegorical symbolism is usually far more obvious - otherwise it wouldn't work: if the commissioner of the portrait intended such an essay on religious faith or truth, then, I think, he would have done so more explicitly. I certainly don't think that an artist of this period would have constructed such a detailed symbolic essay with the intention that no-one would discover what he was up to. This is the opposite of what paintings were meant to do: Even if the commission was a private one, intended to voice concerns about the Henrician settlement, then you would expect more obvious (even if symbolic) additions to this portrait to signify this.
In response to some of the suggested allegorical signifiers in Canon Russ' notes, I would again state that most of the details in this painting have many and varied possible meanings. Overall, there is no explicit and unequivocal message of Catholic or even an overt religious message of any sort: each and every one of the possible details could mean something else or nothing at all. The pillar is a common symbol of strength (often spiritual but not exclusively so); the chipped masonry often an expression of an artist's command of realism, and much of the architectural detail simply a reflection of contemporary design. The 'ruins' in the background are certainly interesting and unusual, but it is difficult to say more than that: I would be particularly reluctant to say anything about the significance of colour and tone without knowing a little more about the painting's physical history (how many times it had been overpainted over the last 500 years: is this background indeed original?)
The Sawston lady could, despite all these reservations, be a portrait of Mary l; although the date of 1537 is very problematic as the dress of the sitter makes this highly unlikely, we know very little about portraits of her as Princess beyond the presumed 'Master John' portrait of 1544. If so, I think it could date from the early 1550's and be just about reconcilable with later portraits of Mary as Queen. On balance, however, I would say that this remains unlikely.
But, the Sawston portrait remains a very rare and very interesting full-length portrait. In a way, for me, the game of indentification is unfortunate, as it suggests that this is all that matters, and detracts more than a little from an appreciation of the painting itself.