so another question I have is that whether it is systematic (a regular pattern) between /a:/ in BrE and /æ:/ in AmE or not.
There are words that a pronounced differently like dance or rather. I have one source which indicates that this contrast is not systematic but restricted to 80 words.
Then there is a passage which I do not understand I cite "For example, while the word pass is pronounced as expected in R.P. (/pa:s/), the word standard has /æ/." - So what exactly is meant by standard since it is written in italic. I also though that in Am it is always the /æ:/ pronunciation and BrE always /a:/
I have thought the entire time that there is a systematic phonological difference!