Last year there was en extensive investigation into the workings centred in Nash Mills, Hemel Hempstead leading to the partial closure of Highbarns road and, as far as I am aware, restrictions to the traffic along Highbarns in conjunction with the existing closure of Pond Road.
The recent investigation was commissioned in light of and in addition to previous investigations carried out in the vicinity of the house on the corner of Highbarns and Pond Road which had sustained subsidence over a period of time due to an apparent 'sink hole/solution feature' in the front garden. This subsidence, coupled with another earlier record of one of the link-houses on the opposite side of Pond Road may have lead to the birth of the theory of a linear sub-terranean feature.
As far as I am aware, the results of the most recent investigation have not yet been published, therefore I am unsure of how much further I can elaborate without consulting certain individuals, but rest assured, there is certainly something worth looking at that down there!!