I seem to recall that the term 'commando boots' referred to the type of sole. At one time British Army boots had leather soles with hobnails, whereas those worn by the Royal Marines had thick rubber soles with plenty of 'grip'- hence the distinction 'commando'. Possibly something to do with hobnails sliding about on ships' decks and steps? Boots with this type of sole were said to have 'commando' soles which became shortened to commando boots, whether they were military surplus or not.
I agree with your description of "commando boots",they weren't military boots and those big chunky rubber soles were screwed on.
I do remember lads wearing ex army boots with leather soles and hobnails in,this would have been in 69 I think,they were kids about 2 years older than me so 13 or 14 in 69.
BTW theres an advert for a high leg version in Spirit of 69,but it must be from later because the boots were £15.99