Ok thats a good source (albeit not very well worded for an aerodrome that has a right hand circuit)
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So if the local ATC authorise a right base join to a left hand circuit its for sure ok.
The local "sky god" who practised this around my way pointed out that he did only turn left once he was in the circuit and therefore conformed with the rules of the air (but, of course, there were no left hand turns for him to make ..) and also that it was only an equivalent to a straight in which few(er) people tend to bitch about.
My guess is that there may be the classic disjoint that so often leads to soooo much debate here between the sentiment of the laws and the interpretation
Must admit, as I said earlier, its not my favourite join but, it is used