The bits in brackets (hopefully obviously!) indicate my second guess/possible substitutions, but after 4-5 listens in a row I'm pretty certain of my 'primary transcript'.

Although the title of the song is Salisbury Plain, I'm certain that the word at the end of line 1 is 'Silbury' -

My interpretation is that Silbury Hill and Frome lie just beyond the edges of Salisbury plain (to the North and West, respectively) - they're part of the wider downland, but the wind blows coldest in the area claimed for military manoeuvres, in the shadow of Stonehenge ('the ragged stones').

For verse 5, I take 'the blues' to be deliberstely multi-layered - the bluestones of Stonehenge; some of the rarer breeds of blue butterfly, adonis blues and chalk hill blues, which have enclaves around Salisbury Plain; and also, a reference to the junctures when the military site was expanded, at times of grave external threat, and regiments like The Blues (the Royal Horse Guards, who were merged with the Royal Dragoons in 1969, and so might have been in Hutchings' mind at the time of writing) may have been welcomed to the plain by the local populace. From a bit of Wikipedia sleuthing I note that in the present day the successor regiment, the Household Cavalry, is garrisoned at the Powle Lines barracks of Bulford Camp, one of 4 major British Army camps on the Plain.