I'm from England, and I think it might be actually either a Scottish accent or someone who probably isn't a native speaker. Its difficult to answer not being able to actually hear the accent. Do you have a link, if its on Youtube?

A lot of regional British speakers do this, so it's hard to pinpoint. My first guess would be northern England, but as I said, the speaker could come from a number of different places. Are you asking in general, or is there a specific recording or video you're listening to?

If by 'op' you mean the /ʊ/ sound in 'book', this is probably a speaker from the North of England. In the more northerly half of England - pretty well everywhere from the Midlands up to the border with Scotland - there are many speakers for whom there is no /ʌ/ sound, as in 'cup' or 'love'. Many speakers from this area use a /ʊ/ sound instead. For example, in standard English, the words 'book' and 'buck' are pronounced differently. 'Book' is pronounced /bʊk/ , whereas 'buck' is pronounced /bʌk/. For many English speakers from the northern half of England, however, these two words are pronounced the same. A person from Manchester, Liverpool, Sheffield or Newcastle, for example, may pronounce 'buck' as /bʊk/ - in other words, with exactly the same pronunciation as 'book'. Other pairs of words which would be pronounced the same in these accents are look/luck and put/putt. Does that help?