Has anyone explained why the remains were only one foot deep? Or why if so shallow they did not surface before?
One of many real mysteries which the documentary ignored in favour of endless obviously staged emoting from the estimable Phillipa. If the body was only 5 feet or so down, with the toings and froings on the site over 500 years, it is quite incredible that only the feet apparently got disturbed/dug up over that time.
Pure conjecture on my part, but the apparent lack of disturbance of the body suggests at least in the period from the demolition of the monastery (usually the wood and stones would be recycled in other building work) to the large scale development of the neighbourhood in Victorian times, the grave was part of the garden of a substantial house - suggests to me that the grave was known to be there and left alone as such. How that knowledge got lost is a mystery for the ages, I suppose.
As to the two major developments as described in the wikipedia entry on Grey Friars, the 19th century development and particularly the 1930s building of the then County Council offices, I can only think it was dumb luck or very shallow foundations!