I think the 75 was introduced in 1977, Robin. Don't know where I read this but it's in the old memory bank somehow. But whether the UK got any in that year I don't know. The examples I have owned or seen have been from '78 onwards.
The 66 is often said to have been introduced in 1974 but I have seen one 1973 example for sale. Can't remember the month but I assume it was late '73.