I am a very experienced teacher. Been teaching for 33 years. Was a head of dept in a large secondary school in the UK until last August. I have a degree and a PGCE (uk equivalent of PGDE I assume?) It is a part time post so pro rata about 2/3's full salary. Not sure of the salary scale as they just offered me an amount and I accepted.
I am not sure Part time posts are common in HK. I just happened to be in the right place at the right time I think!
On the other hand, there are more and more reports that the teaching conditions back in the UK are deteriorating. I can understand why some might want to get away and try something new, even if that meant a (temporary) reduction in income.